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HOW  CROPS   FEED. 


A  TREATISE  ON  THE 


ATMOSPHERE     AND     THE     SOIL 


AS    BELATED   TO    THE 


Nutrition  of  Agricultural  Plants. 


WITH    ILLUSTRATIONS. 


SAMUEL  W.  JOHNSON^,  M.A., 

PBOPESSOR    OF    AXALYTICAL    AND    AGBICTTLTUKAL    CHEMISTEY    IX    THE    SHEFFIELD 
SCIENTIFIC    SCHOOL    OF    YALE    COLLEGE  ;    CHEMIST    TO    THE   CONNEC- 
TICUT   STATE    AGRICULTURAL    SOCIETY;    MEMBER    OF    THE 
NATIONAL  ACADEMY  OF  SCIENCES. 


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NEW    YORK: 
ORANGE    JITDD    COMPANY, 


245     B 


ROADWAY.  ^,   TTHliAH^ 


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MASS" 


Entered  according  to  Act  of  Congress,  in  the^  year  1870,  by 
ORANGE    JUDD    &    CO., 

In  the  Clerk's  Office  of  the  District  Court  of  the  United  States  for  the  Southern 
District  of  New  York. 


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PREFACE. 


The  work  entitled  "  How  Crops  Grow "  has  been  re- 
ceived with  favor  beyond  its  merits,  not  only  in  America, 
but  in  Europe.  It  has  been  republished  in  England  under 
the  joint  Editorship  of  Professors  Church  and  Dyer,  of 
the  Royal  Agricultural  College,  at  Cirencester,  and  a 
translation  into  German  is  soon  to  appear,  at  the  instiga- 
tion of  Professor  von  Liebig. 

The  Author,  therefore,  j^uts  forth  this  volume — the  com- 
panion and  complement  to  the  former — with  the  hope  that 
it  also  will  be  welcomed  by  those  who  appreciate  the  sci- 
entific aspects  of  Agriculture,  and  are  persuaded  that  a 
true  Theory  is  the  surest  guide  to  a  successful  Practice. 

The  writer  does  not  flatter  himself  that  he  has  produced 
a  popular  book.  He  has  not  sought  to  excite  the  imagi- 
nation with  high- wrought  pictures  of  overflowing  fertility 
as  the  immediate  result  of  scientific  discussion  or  experi- 
ment, nor  has  he  attempted  to  make  a  show  of  revolution- 
izing his  subject  by  bold  or  striking  speculations.  His 
office  has  been  to  digest  the  cumbrous  m.ass  of  evidence, 

in  which  the  truths  of  Vegetable  Nutrition  lie  buried  out 
5 


VI  PREFACE. 

of  the  reach  of  the  ordinary  inquirer,  and  to  set  them 
forth  in  proper  order  and  in  plain  dress  for  their  legiti- 
mate and  sober  uses. 

It  has  cost  the  Investigator  severe  study  and  labor  to 
discover  the  laws  and  many  of  the  facts  which  are  laid 
down  in  the  following  pages.  It  has  cost  the  Author  no 
little  work  to  collect  and  arrange  the  facts,  and  develop 
their  mutual  bearings,  and  the  Reader  must  pay  a  similar 
price  if  he  would  apprehend  them  in  their  true  signifi- 
cance. 

In  this,  as  in  the  preceding  volume,  the  Author's  method 
has  been  to  bring  forth  all  accessible  facts,  to  present  their 
evidence  on  the  topics  under  discussion,  and  dispassion- 
ately to  record  their  verdict.  If  this  procedure  be  some- 
times tedious,  it  is  always  safe,  and  there  is  no  other  mode 
of  treating  a  subject  which  can  satisfy  the  earnest  inquirer. 

It  is,  then,  to  the  Students  of  Agriculture,  wliether  on  the 
Farm  or  in  the  School,  that  the  Author  commends  his 
book,  in  confidence  of  receiving  full  sympathy  for  its 
spirit,  whatever  may  be  the  defects  in  its  execution. 


CONTENTS. 


iNTBODtrCTION 17 

DIVISION    I. 

THE  ATMOSPHERE  AS  EELATED  TO  VEGETATION. 

CHAPTER     I . 

Atmospheric  Air  as  the  Food  of  Plants. 

§    1.  Chemical  Composition  of  the  Atmosphere 21 

§    2.  Relation  of  Oxygen  Gas  to  Vegetable  Nutrition 22 

§    3.  "        "  Nitrogen  Gas  to        "  "        26 

§    4,         "        "  Atmospheric  Water  to  Vegetable  Nutrition 34 

§    5.         "        "  Carbonic  Acid  Gas    "  "  "        38 

§6.  4        u  Atmospheric  Ammonia  to    "  "        49 

§    7.  Ozone 03 

§    8.  Compounds  of  Nitrogen  and  Oxygen  in  the  Atmosphere 70 

§    9.  Other  Ingredients  of  the  Atmosphere 91 

§  10.  Recapitulation  of  the  Atmospheric  Supplies  of  Food  to  Crops 94 

§  11.  Assimilation  of  Atmospheric  Food 97 

§  12.  Tabular  View  of  the  Relations  of  the  Atmospheric  Ingredients  to  the 
Life  of  Plants 98 

CHAPTER     II. 

The  Atmosphere  as  Physicallt  Related  to  Vegetation. 

§  1.  Manner  of  Absorption  of  Gaseous  Food  by  Plants , , 99 

DIVISION    II. 

THE  SOIL  AS  RELATED  TO  VEGETABLE  PRODUCTION. 

CHAPTER     I. 

Introductory 104 


VIII  HOW    CROPS    FEED. 

CHAPTEE    II. 
Origin  and  Formation  of  Soils 106 

§  1.  Chemical  Elements  of  Eocks lOT 

§  2.  Mineral ogical  Elements  of  Eocks  108 

§  3.  Eocks,  their  Kinds  and  Characters 117 

§  4.  Conversion  of  Eocks  into  Soil  122 

§  5.  Incorporation  of  Organic  Matter  with  the  Soil,  and  its  Eflccts 135 

CHAPTEE     III. 
Kinds  of  Soils,  their  Definition  and  Classification. 

§  1.  Distinctions  of  Soils  based  upon  the  Mode  of  their  Formation  or  Deposi- 
tion   142 

§  2.  Distinctions  of  Soils  based  upon  Obvious  or  External  Characters 146 

CHAPTEE    IV. 
Physical  Characters  of  the  Soil 157 


§  1.  Weight  of  Soils 158 

§  2.  State  of  Division 159 

§  3.  Absorption  of  Vapor  of  Water 161 

§  4.  Condensation  of  Gases 165 

§  5.  Power  of  Eemoving  Solid  Matters  from  Solution 171 

§  6.  Permeability  to  Liquid  Water.    Imbibition.     Capillary  Power 176 

§  7.  Changes  of  Bulk  by  Drying  and  Frost 183 

§  8.  Adhesiveness 184 

§  9.  Eelations  to  Heat 186 

CHAPTEE    V. 

The  Soil  as  a  Source  of  Food  to  Crops  :   Ingredients  whose  Elements 
ARE  of  Atmospheric  Origin. 

§  1.  The  Free  Water  of  the  Soil  in  its  Eelations  to  Vegetable  Nutrition 199 

§  2.  The  Air  of  the  Soil 217 

§  3.  Non-nitrogenous  Organic  Matters.     Humus 222 

§  4.  The  Ammonia  of  the  Soil 238 

§  5.  Nitric  Acid  (Nitrates)  of  the  Soil 251 

§  6.  Nitrogenous  Organic  Matters  of  the  Soil.    Available  Nitrogen 274 

§  7.  Decay  of  Organic  Matters 289 

§  8.  Nitrogenous  Principles  of  Urine 293 

§  9.  Comparative  Nutritive  Value  of  Ammonia-Salts  and  Nitrates 300 


CONTENTS.  IX 

CHAPTER     VI. 

The  Soil  as  a  SorRCE  of  Food  to  Crops  :    Ingredients  whose  Elements 
ARE  Derived  frok  Rocks. 

§  1.  General  View  of  the  Constitution  of  the  Soil  as  Related  to  Vegetable 

Nutrition 305 

§  2.  Aqueous  Solution  of  the  Soil 309 

§  3.  Solution  of  the  Soil  in  Strong  Acids 329 

§  4.  Portion  of  Soil  Insoluble  in  Acids 330 

§  5.  Reactions  by  which  the  Solubility  of  the  Elements  of  the  Soil  Is  al- 
tered.    Solvent   Effects  of  Various  Substances.     Absoi-ptive  and 

Fixing  Power  of  Soils 331 

§  6.  Review  and  Conclusion 361 


INDEX. 


Absorption  and   displacement,  law 

of 33(5 

Absorptive  power  of  soils 333 

"         "  cause  of.343,  354 
"  "         "    significance 

of 874 

Acids  in  soil 223 

"      absorbed  by  soils 355 

Adhesion 165 

Adhesiveness  of  soils 184 

Air,  atmospheric,  composition  of..  21 
"    within  the  plant,  composition 

of 45 

Alkali-salts,  solvent  effect  of 130 

Allotropism C6 

Alluvium 145 

Aluminum,  alumina 107 

Amides 276 

Amide-like  bodies 277,  300 

Ammonia 49,  54 

"         absorbed  by  clay. . .  .243,  267 

"  "         '^  peat 360 

"  "         "  plants.... 56,  98 

"         condensed  in  soils 240 

"         conversion  of  into  nitric 

acid 85 

"         evolved  from  flesh  decay- 
ing under  charcoal 169 

"         fixed  by  gypsum 244 

"         in  atmosphere 54 

"         "  "    how  formed.77,  85 

"         of  rain,  etc 60 

"         of  the  soil,  formation  of. 239 
"  "         "  chemically 

combined.  243 
"  "         "  physically 

condensed. 240 

"  "         "     quantity  of.. 248 

"     solubility  of.  246 

"  "         "     TolatiliTy  of..244 

11 


Ammonia-salts  and  nitrates,  nutri- 
tive value  of 300 

Amphibole 112 

Analysis  of  soils,  chemical  indica- 
tions of ...368 

"     mechanical 147 

Apatite 116 

Apoci'enatcs 231 

Apocrenic  acid 227,  229 

Argillite 119 

Ash-ingredients,    quantity   needful 

for  crops 363 

Atmosphere,     chemical     composi- 
tion  21,  22 

"  physical  constitution..  99 

Atmospheric  food,  absorbed 99 

"  "     assimilated  —  97 

Barley  crop,  ash  ingredients  of. 364 

Basalt 120 

Bases,  absorbed  by  soils 335,  359 

Bisulphide  of  iron 115 

Burning  of  clay , 185 

Calcite 115 

Capillarity 175,  199,  201 

Carbohydrates  in  soil 222 

Carbon,  fixed  by  plants 43,  48 

"       in  decay 291 

"        supply  of 95 

Carbonate  of  lime ...  115,  163 

"  "  magnesia 115,162 

Carbonic  acid ..,..: 38 

"  "  absorbed  by  soil 221 

"  "  "         "  plants.41, 

45,  98 
"  "  exhaled  by  plants.. 43,  99 

"  "  in  the  soil 218 

'■'■  "      "      water  of  soil.. 220 

"  "  quantity  in  the  air.40, 

47,  94 
"  "  solubility  in  water. 40, 130 


XII 


HOW    CROPS    FEED. 


Carbonic  acid,  solvent  action  of 128 

Carbonic  oxide 93 

Chabasite 115 

"         action    on    saline    com- 
pounds  345 

"         formed  in  Roman  mason- 
ry  351 

Chalk  soils 192 

Charcoal,  absorbs  gases 165 

"         defecating  action  of. 1T4 

Chili  saltpeter 253 

Chlorite 113 

Chrysolite 114 

Clay 132,  134,  154 

"  absorptive  power 174 

"  eflFect  of,  on  mine 293 

Clay-Blate 119 

Coffee,  condenses  gases 168 

Color  of  soil 190 

Conglomerates.. 121 

Crenates 231 

Crenic  acid 227,  229 

Decay 289 

Deliquescence 163 

Deserts 197 

Dew 189, 195 

Diffusion  of  gases 100 

Diorite 120 

Dolerite 120 

Dolomite 115,  121 

Di'aining 185 

Drain  water,  composition  of 312 

Drift 144 

Dye  stuffs,  fixing  of 174 

Earth-closet 171 

Eremacausis 289 

Evaporation,  produces  cold 188 

"  amount  of,  from  soil.  197 

Exhalation 202,  206 

Exposure  of  soil 195 

Feldspar 108 

"       growth  of  barley  in 160 

Fermentation 290 

Fixtation  of  Ijases  in  the  soil 339 

Frost,  effects  of,  on  rocks 124 

''  on  soils 184,185 

Fumicacid 258 

Gases,  absorbed  by  the  plant 103 

"  "         "  porous  bodies.. 167 

"  "         "  soils 165,  166 

"        diffusion  of 100 

"       osmose  of 102 

Glaciers 124 


Glycine 296 

Glycocoll    296 

Gneiss... 119 

Granite 118,  120 

Gravel 152 

"     warmth  of 195 

Guanin 296 

Gypsum 115 

"       does    not    directly  absorb 

water 162 

"       fixes  ammonia 244 

Hardpan 156 

Heat,  absorption  and  radiation  of. . 

188,  193 

"     developed  in  flowering 24 

"      of  soil 187 

Hippuric  acid 295,  277 

Hornblende 112 

Hydration  of  minerals 127 

Hydraulic  cement 122 

Hydrochloric  acid  gas 93 

Hydrogen,  supply  of,  to  plants 95 

"■  in  decay 291 

Hydrous  silicates,  formation  of 352 

Hygroscopic  quality 164 

Humates 230 

Humic  acid 226,  229 

Humin 236,  229 

Humus 136,  224,  276 

"     absorbent  power  for  water. .  163 
"     absorbs  salts  from  solutions.  172 

"■     action  on  minerals 138 

"     chemical  nature  of 133 

"     does  it  feed  the  plant  ? 232 

"     not  essential  to  crops 238 

"     value  of 183 

Iodine  in  sea-water 322 

Isomorphism Ill 

Kreatin 196 

Kaolinite 113,132 

Latent  heat 188 

Lawes'  and  Gilbert's  wheat  experi- 
ments  372 

Leucite 113 

Lime,  effects  of .184, 185 

Limestone 121,  122 

Loam 154 

Lysimeter 314 

Magnesite 115 

Marble  ....v 121 

Marl 155 

Marsh  gas 91,  99 

Mica 109 


INDEX. 


XIII 


Mica  slate ,   119 

Minerals 106,  lOS 

"       hydration  of. 127 

"        solution  of 127 

"       variable  composition  of. . ..110 
Moisture,  effect  of,  on  temperature 

of  soil 195 

Mold 15G 

Moor-bedpan 1.57 

Muck 155 

Nitrate  of  ammonia 71,  73 

"         "         "        in  atmosphere.  89 

Nitrates 252 

"        as  food  for  plants 271 

"        formed  in  soil. 171,179 

"        in  water 270 

"       loss  of. 270 

"        reduction  of. 73,  82,  85 

"  "  "  in  soil 268 

"       tests  for 75 

Nitric  acid 70 

"        "  as  plant-food 90,98 

"       "  deportment  towards   the 

soil 357 

"        "  in  atmosphere 86 

"        "    "  rain-water 86 

"    "   soil 251,  254 

'^        "    "     "■  sources  of 256 

Nitric  oxide 72 

Nitric  peroxide 72 

Nitrification 252,  286 

"  conditions  of 265,  292 

Nitrogen,  atmospheric    supply    to 

plants 95 

"  combined,  in  decay. 291,  292 

"  "  of  the  soil... 275 

"  combined,   of    the    soil, 

available 283 

"  combined,   of    the    soil, 

inert 278 

"  combined,  of    the    soil, 

quantity  needed  for  crops. 288 
"  free,  absorbed  by  soil. .  .167 

"  "    assimilated   by  the 

soil 259 

"  "    in  soil 218 

"  "    not     absorbed     by 

vegetation 26,  99 

"             "    not  emitted  by  liv- 
ing plants 23 

Nitrogen-compounds,  formation  of, 

in  atmosphere. 75,  77,  83 


Nitrogenous   fertilizers,    effect    on 

cereals ...  83 
Nitrogenous  organic  matters  of  soil. 274 

Nitrous  acid  72 

Nitrous  oxide 71,  93 

Ocher 156 

Oxidation,  aided  by  porous  bodies. 

169, 170 

Oxide  of  iron,  a  carrier  of  oxygen.  .257 

"  "         hydrated,in  the  soil.350 

Oxj'^gen,  absorbed  by  plants 98 

"         essential  to  growth 23 

' '         exhaled  by  foliage 25,  99 

"         function  of,  in  growth 24 

"         in  soil 218 

'•         supply 94 

"         weathering  action  of 131 

Ozone , 63 

"    concerned  in  oxidation  of  ni- 
trogen   82 

"    formed  by  chemical  action. 66,  67 
"    produced  by  vegetation. 67, 84,  99 
"    relations  of,  to  vegetable  nu- 
trition.   70 

Pan,  composition  of 352 

Parasitic  plants,  nourishment  of. .  .235 

Peat 155,224 

"  nitrogen  of 274 

Phosphate  of  lime IIG 

Phosphoric  acid  fixed  by  the  soil . .  .357 
"  "    presence     in    soil 

Avater 315 

Phosphorite IIG 

Plant-food,  concentration  of. 320 

"  maintenance  of  supply. 371 

Platinized  charcoal 170 

Platinum  sponge,  condenses  oxygenl70 

Porphyry 120 

Potash,  quantity  in  barley  crop 363 

Provence,  drouths  of 198 

Pyrites 115 

Pyroxene 112 

Pumice 120 

Putrefaction .- 290 

Quartz 108,  122 

Rain-water,  ammonia  in 60,  88 

"  nitric  acid  in 86 

"  phosphoric  acid  in 94 

Ree  Ree  bottom,  soil  of 160 

Respiration  of  the  plant 43 

Rocks 106,  117 

"    attacked  by  plants. 140 


XTY 


HOW    CEOPS   PEED. 


Rocks,  conversion  into  soils 122 

Hoots,  direct  action  on  soil 326 

Saline  incrustations 179 

Saltpeter 252 

Salts  decomposed  or  absorbed  by 

the  soil 336 

Sand 153,162 

Sand  filter 172 

Sandstone 121 

Serpentine 114,  121 

Schist,  micaceous 119 

"■       talcose 121 

'•        chlorite 121 

Shales 122 

Sherry  wine  region 192 

Shrinking  of  soils ." . .  183 

Silica 108 

"     function  in  the  soil 353 

'*     of   soil,  liberated   by    strong 

acids  330 

Silicates 109 

"        zeoli tic,  presence  in  soils.. 349 

Silicic  acid,  fixed  in  the  soil 358 

Silk,  hygroscopic 165 

Soapstone 121 

Sod,  temperature  of 199 

Soil 104 

"  absorptive  power  of 333 

"  aid  to  oxidation 170 

"  aqueous  solution  of 309,  323,  328 

"  condenses  gases 165,  166 

"  capacity  for  heat 194 

"  chemical  action  in 331 

*'  composition  of. 362,  869 

"  exhaustion  of. 373 

"  inert  basis 305 

"  natural  strength  of. . ., 372 

"  origin  and  formation..  106,  122,  135 

"  physical  characters 157 

"  porosity  of. 176 

"  portion  insoluble  in  acids 330 

"  relative  value  of  ingredients 367 

"  reversion  to  rock 332 

"  solubility  in  acids 329 

"  "  water 309 

"  source  of  food  to  crops 305 

"  state  of  division 159 

Soils,  sedentary 143 

"      transported 143 

"      weight  of 158 

Solubility,  standards  of 308 


Solution  of  soil  in  acids 370 

"  "        "  water 310 

Steatite 121 

Swamp  muck 155 

Sulphates,  agents  of  oxidation 258 

Sulphate  of  lime 115 

Sulphur,  in  decay 293 

Sulphtirous  acid 94 

Sulphydric  acid 94 

Syenite 120 

Talc 113 

Temperature  of  soil 186,  187,  194 

Transpiration 202,  208 

Trap  rock 120 

Ulmates 230 

Ulmic  acid .224,  226,  229 

Ulmin 224,  226,  229 

Urea 294,  277 

Uric  acid 295,  277 

Urine 293 

"     preserved  fresh  by  clay 293 

"     its  nitrogenous  principles  as- 
similated by  plants 296 

Vegetation,  antiquity  of 138 

"  decay  of. 137 

"  action  on  soil 140 

Volcanic  rocks,  conversion  to  soil..  135 

Wall  fruits 199 

Water  absorbed  by  roots 202,  210 

"     functions  of,  in  nutrition  of 

plant 216 

"     imbibed  by  soil 180 

"     movements  in  soil 177 

"     proportion  of  in  plant,  influ- 
enced by  soil 213 

'■■      of  soil 315,  317 

"         "      bottom  water 200 

'^     capillary 200 

••     hydrostatic 199 

"     hygroscopic 201 

"     quantity  favorable  to  crops.  .214 

Water-currents 124 

Water-vapor,  absorbed  by  soil. 161, 164 

"  exhaled  by  plants 99 

"  not      absorbed       by 

plants 35,  99 

"  of  the  atmosphere 34 

Weathering 131-134 

Wilting 203 

Wool,  hygroscopic 164 

Zeolites 114,349 


HOW    CROPS    FEED 


H0¥  CROPS  FEED. 


IN^TRODUCTIOI^. 


In  his  treatise  entitled  "  How  Crops  Grow,"  the  author 
has  described  in  detail  the  Chemical  Composition  of  Agri- 
cultural Plants,  and  has  stated  what  substances  are  indis- 
pensable to  their  growth.  In  the  same  book  is  given  an 
account  of  the  apparatus  and  processes  by  which  the  plant 
takes  up  its  food.  The  sources  of  the  food  of  crops  are, 
however,  noticed  there  in  but  the  briefest  manner.  TIiq 
present  work  is  exclusively  occupied  with  the  important 
and  extended  subject  of  Vegetable  IsTutrition,  and  is  thu^ 
the  complement  of  the  first-mentioned  treatise.  Whatever 
information  may  be  needed  as  preliminary  to  an  under^ 
standiug  of  this  book,  the  reader  may  find  in  "How  Crop^ 
Grow."  * 

That  crops  grow  by  gathering  and  assimilating  food  is 
a  conception  with  which  all  are  familiar,  but  it  is  only  by 
following  the  subject  into  its  details  that  we  can  gain  hinta 
that  shall  apply  usefully  in  Agricultural  Practice. 


*  It  has  been  at  least  the  author's  aim  to  make  the  first  of  this  series  of  books, 
prepare  the  way  for  the  second,  as  both  the  first  and  the  second  are  written  ta 
make  possible  an  intelligible  account  of  the  mode  of  action  of  Tillage  and  of 
Fertilizers,  which  will  be  the  subject  of  a  third  work. 

17 


18  HOYf    CHOPS    FEED. 

When  a  seed  germinates  in  a  medium  tliat  is  totally- 
destitute  of  one  or  all  the  essential  elements  of  the  plant, 
the  embryo  attains  a  certain  development  from  the  mate- 
rials of  the  seed  itself  (cotyledons  or  endosperm,)  but 
shortly  after  these  are  consumed,  the  plantlet  ceases  to  in- 
crease in  dry  y/eight,*  and  dies,  or  only  grows  at  its  own 
expense. 

A  similar  seed  deposited  in  ordinary  soil,  watered  with 
rain  or  spring  water  and  freely  exposed  to  the  atmosphere, 
evolves  a  seedling  which  survives  the  exhaustion  of  the 
cotyledons,  and  continues  without  cessation  to  grow, 
forming  cellulose,  oil,  starch,  and  albumin,  increases  many 
times — a  hundred  or  two  hundred  fold — in  weight,  runs 
normally  through  all  the  stages  of  vegetation,  blossoms, 
and  yields  a  dozen  or  a  hundred  new  seeds,  each  as  perfect 
as  the  original. 

It  is  thus  obvious  that  Air,  Water,  and  Soil,  are  capa- 
ble of  feeding  plants,  and,  under  purely  natural  conditions, 
do  exclusively  nourish  all  vegetation. 

In  the  soil,  atmosphere,  and  w^ater,  can  be  found  no 
trace  of  the  peculiar  organic  principles  of  plants.  We 
look  there  in  vain  for  cellulose,  starch,  dextrin,  oil,  or  al- 
bumin. The  natural  sources  of  the  food  of  crops  consist 
of  various  salts  and  gases  which  contain  the  ultimate  ele- 
ments of  vegetation,  but  which  require  to  be  collected  and 
worked  over  by  the  j^lant. 

The  embryo  of  the  germinating  seed,  like  the  bud  of  a 
tree  when  aroused  by  the  spring  warmth  from  a  dormant 
state,  or  like  the  sprout  of  a  potato  tuber,  enlarges  at  the 
expense  of  previously  organized  matters,  supplied  to  it 
by  the  contiguous  ^^arts. 

As  soon  as  the  plantlet  is  weaned  from  the  stores  of  the 


*  Since  vegetable  matter  may  contain  a  variable  amount  of  water,  either  tliat 
which  belongs  to  the  sap  of  the  fresh  plant,  or  that  which  is  hygroscopically  re- 
tained in  the  pores,  all  comparisons  must  be  made  on  the  dr'y^  i.  e.,  tvater-free 
substance.    See  "How  Crops  Grow,"  pp.  53-5. 


IXTRODUCTION.  19 

mother  seed,  the  materials,  as  well  as  the  mode  of  its  nu- 
trition, are  for  the  most  part  completely  changed.  Hence- 
forth the  tissues  of  the  plant  and  the  cell-contents  must 
be  principally,  and  may  be  entirely,  built  up  from  purely 
inorganic  or  mineral  matters. 

In  studying  the  nutrition  of  the  plant  in  those  stages 
of  its  growth  that  are  subsequent  to  the  exhaustion  of  the 
cotyledons,  it  is  needful  to  investigate  separately  the  nu-^ 
tritive  functions  of  the  Atmosphere  and  of  the  Soil,  for 
the  important  reason  that  the  atmosphere  is  nearly  con- 
stant in  its  composition,  and  is  beyond  the  reach  of  human 
influence,  v/hile  the  soil  is  infinitely  variable  and  may  be 
exhausted  to  the  verge  of  unproductiveness  or  raised  to 
the  extreme  of  fertility  by  the  arts  of  the  cultivator. 

In  regard  to  the  Atmosphere,  we  have  to  notice  minutely 
the  influence  of  each  of  its  ingredients,  including  Water 
in  the  gaseous  form,  upon  vegetable  production. 

The  evidence  has  been  given  in  "  How  Crops  Grow,"  which 
establishes  what  fixed  earthy  and  saline  matters  are  essential 
ingredients  of  plants.  The  Soil  is  plainly  the  exclusive 
source  of  all  those  elements  of  vegetation  which  cannot  as- 
sume the  gaseous  condition,  and  which  therefore  cannot  ex- 
ist in  the  atmosphere.  The  study  of  the  soil  involves  a  con- 
sideration of  its  origin  and  of  its  manner  of  formation.  The 
productive  soil  commonly  contains  atmospheric  elements, 
which  are  imj^ortant  to  its  fertility ;  the  mode  and  extent 
of  their  incorporation  with  it  are  topics  of  extreme  prac- 
tical importance.  We  have  then  to  examine  the  signif- 
icance of  its  water,  of  its  ammonia,  and  especially  of  its 
nitrates.  These  subjects  have  been  recently  submitted  to 
extended  investigations,  and  our  treatise  contains  a  large 
amount  of  information  pertaining  to  them,  which  has  never 
before  appeared  in  any  publication  in  the  English  tongue. 

Those  characters  of  the  soil  that  indirectly  afiect  the 
growth  of  plants  are  of  the  utmost  moment  to  the  farm- 
er.    It  is  through  the  soil  that  a  supply  of  solar  heat,  with- 


20  HOW    CKOPS    FEED. 

out  which  no  life  is  possible,  is  largely  influenced.  Water, 
whose  excess  or  deficiency  is  as  pernicious  as  its  proper 
quantity  is  beneficial  to  crops,  enters  the  plant  almost 
exclusively  through  its  roots,  and  hence  those  qualities 
of  the  soil  which  are  most  favorable  to  a  due  supply  of 
this  liquid  demand  careful  attention.  The  absorbent  pow- 
er of  soils  for  the  elements  of  fertilizers  is  a  subject  which 
is  treated  of  with  considerable  fullness,  as  it  deserves. 

Our  book  naturally  falls  into  two  divisions,  the  first  of 
which  is  devoted  to  a  discussion  of  the  Relations  of  the 
Atmosphere  to  Vegetation,  the  second  being  a  treatise  on 
the  Soil. 


DIVISION  I. 


THE    ATMOSPHERE    AS    RELATED    TO 
VEGETATION. 

CHAPTER,     I. 

ATMOSPHERIC    AIR   AS    THE   FOOD   OF    PLANTS. 

§  1. 
CHEMICAL  COMPOSITION  OF  THE  ATMOSPHERE. 

A  multitude  of  observations  has  demonstrated  that 
from  ninety-five  to  ninety-nine  per  cent  of  the  entire  mass 
(weight)  of  agricultural  plants  is  derived  directly  or  indi- 
rectly from  the  atmosj^here. 

The  general  composition  of  the  Atmosphere  is  familiar 
to  all.  It  is  chiefly  made  up  of  the  two  elementary  gases, 
Oxygen  and  Mtrogen,  which  have  been  described  in  "How 
Crops  Grow,"  pp.  33-39.*  These  two  bodies  are  present 
in  the  atmosphere  in  very  nearly,  though  not  altogether, 
invariable  proportions.  Disregarding  its  other  ingredients, 
the  atmosphere  contains  in  100  parts 

By  weight.  By  volume. 

Oxygen 23.1?  20.95 

Nitroffeu 76.83  79.05 


100.00  100.00 

Besides  the  above  elements,  several  other  substances  oc- 


*  In  our  frequent  references  to  this  book  we  shall  employ  the  abbreviation 
H.  C.  G. 

21 


22  HOW    CEOPS    FEED. 

cur  or  may  occur  iu  the  air  in  minute  and  variable  quanti- 
ties, viz. : 

Water,  as  vapor. .  .average  proportion  Id}-  weight,             i  ]ioo 

Carbonic  acid  gas        "  "             "        "               ^|io-ooo 

Ammonia                     "  "             "        "          Mso-ooo-ooo? 

Ozone                            "  "             "        "    minute  traces. 

Nitric  acid                    "  "             "        "          "          " 

Nitrous  acid                 "  "             "        "          "           " 

Marsli  gas                     "  "             "        ''          '<          " 

In  air  of  (^^'■^°'^^^^^^^®'  "  "  "        " 

■<  Sulpliurous  acid,          "  "  "        "  "  "       ' 

towns.    (  saipbydric  acid 

Miller  gives  for  the  air  of  England  the  following  aver- 
age proportions  by  volume  of  the  four  most  abundant  in- 
gredients.— [Elements  of  Chemistry^  part  II.,  p.  30,  3d  Ed.) 

Oxygen 20.61 

Nitrogen 77.95 

Carbonic  acid 04 

Water-vapor 1.40 

100.00 
We  may  now  appropriately  proceed  to  notice  in  order 
each  of  the  ingredients  of  the  atmosphere  in  reference  to 
the  question  of  vegetable  nutrition.  This  is  a  subject  re- 
garding Avhich  unaided  observation  can  teach  us  little  or 
nothing.  The  atmosphere  is  so  intangible  to  the  senses 
that,  without  some  finer  instruments  of  investigation,  we 
should  forever  be  in  ignorance,  even  of  the  separate  exist- 
ence of  its  two  principal  elements.  Chemistry  has,  how- 
ever, set  forth  in  a  clear  light  many  remarkable  relations 
of  the  Atmosphere  to  the  Plant,  whose  study  forms  one 
of  the  most  instructive  chapters  of  science. 


RELATIONS  OF  OXYGEN   GAS  TO   VEGETABLE   NUTRITION. 

Absorption  of  Oxygen  Essential  to  Growtli. — The  ele- 
ment Oxygen  is  endowed  with  great  chemical  activity. 
This  activity  we  find  exhibited  in  the  first  act  of  vegeta* 


AT]\I0SPHEEIC    AIR   AS    THE    FOOD    OF    PLANTS. 


23 


tion,  viz.:  in  germination.  We  know  that  the  presence  of 
oxygen  is  an  indispensable  requisite  to  the  sprouting  seed, 
and  is  possibly  the  means  of  provoking  to  action  the  dor- 
mant life  of  the  germ.  The  ingenious  experiments  of  Traube 
(H.  C.  G-.,  p.  326.)  demonstrate  conclusively  that  free 
oxygen  is  an  essential  condition  of  the  growth  of  the 
seedling  plant,  and  must  have  access  to  the  plumule,  and 
especially  to  the  parts  that  are  in  the  act  of  elongation. 

De  Saussure  long  ago  showed  that  oxygen  is  needful  to 
the  development  of  the  buds  of  maturer  plants.  He  ex- 
perimented in  the  following  manner :  Several  woody  twigs 
(of  willow,  oak,  apple,  etc.)  cut 
in  spring-time  just  before  the 
buds  should  unfold  were  placed 
under  a  bell-glass  containing 
common  air,  as  in  iig.  1.  Their 
cut  extremities  stood  in  v>^ater 
held  in  a  small  vessel,  while  the 
air  of  the  bell  was  separated 
from  the  external  atmosphere  by 
the  mercury  contained  in  the 
large  basin.  Thus  situated,  the 
buds  opened  as  in  the  free  air, 
and  oxygen  gas  was  found  to  be 
consumed  in  considerable  quan- 
tity. When,  however,  the  twigs  were  confined  in  an 
atmosphere  of  nitrogen  or  hydrogen,  they  decayed,  with- 
out giving  any  signs  of  vegetation.  {Mecherches  sur  la 
Yegetatlon,  p.  115.) 

The  same  acute  investigator  found  that  oxj^genis  ab- 
sorbed by  the  roots  of  plants.  Fig.  2  shows  the  arrange- 
ment by  which  he  examined  the  effect  of  different  gases 
on  these  organs.  A  young  horse-chestnut  plant,  carefully 
lifted  from  the  soil  so  as  not  to  injure  its  roots,  had  the 
latter  passed  through  the  neck  of  a  bell-glass,  and  the  stem 
was  then  cemented  air-tight  into  the  opening.     The  bell 


Fio-.  1. 


24 


HOW    CROPS    FEED. 


was  placed  in  a  basin  of  mercury,  C,  D,  to  shut  off  its  con- 
tents from  the  external  air.  So  much  water  was  intro- 
duced as  to  reach  the  ends  of  the  j^rincipal  roots,  and  the 
space  above  was  occupied  by  com- 
mon or  some  other  kind  of  air.  In 
one  experiment  carbonic  acid,  in  a 
second  nitrogen,  in  a  third  hydro- 
gen, and  in  three  others  common 
air,  was  employed.  In  the  first  the 
roots  died  in  seven  or  eight  days, 
in  the  second  an4  third  they  perish- 
ed in  thirteen  or  fourteen  days, 
while  in  the  three  others  they  re- 
mained healthy  to  the  end  of  three 
weeks,  when  the  experiments  were 
concluded.  {Recherches,  p.  104.) 
Flowers  require  oxygen  for  their 
development.  Aquatic  plants  send 
their  flower-buds  above  the  water 
to  blossom.  De  Saussure  found 
that  flowers  consume,  in  24  hours, 
several  or  many  times  their  bulk  of  oxygen  gas.  This 
absorption  proceeds  most  energetically  in  the  pistils  and 
stamens.  Flowers  of  very  rapid  growth  experience  in 
this  process,  a  considerable  rise  of  temperature.  Garreau, 
observing  the  spadix  of  Arwn  italicum,  which  absorbed 
28|-  times  its  bulk  of  oxygen  in  one  hour,  found  it  15°  F. 
warmer  than  the  surrounding  air.  In  the  ripening  of 
fruits,  oxygen  is  also  absorbed  in  small  quantity. 

The  Function  of  Free  Oxygen. — All  those  processes 
of  growth  to  which  free  oxygen  gas  is  a  requisite  appear 
to  depend  upon  the  transfer  to  the  growing  organ  of  mat- 
ters previously  organized  in  some  other  part  of  the  plant, 
and  probably  are  not  cases  in  which  external  inorganic 
bodies  are  built  up  into  ingredients  of  the  vegetable  struc- 
ture.    Young  seedlings,  buds,  flowers,  and  ripening  fruits, 


Fig.  3. 


ATMOSPHEEIG    AIR    AS    THE    FOOD    OF    PLANTS.  25 

have  no  power  to  increase  in  mass  at  the  expense  of  the 
atmosphere  and  soil;  they  have  no  provision  for  the  ab- 
sorption of  the  nutritive  elements  that  surround  them  ex- 
ternally, but  grow  at  the  expense  of  other  parts  of  the  plant 
(or  seed)  to  which  they  belong.  The  function  of  free 
gaseous  oxygen  in  vegetable  nutrition,  so  far  as  can  be 
judged  from  onr  existing  knowledge,  consists  in  effecting 
or  aiding  to  effect  the  conversion  of  the  materials  which 
the  leaves  organize  or  which  the  roots  absorb,  into  the 
proper  tissues  of  the  growing  parts.  Free  oxygen  is  thus 
probably  an  agent  of  assimilation.  Certain  it  is  that  the 
free  oxygen  which  is  absorbed  by  the  plant,  or,  at  least,  a 
corresponding  quantity,  is  evolved  again,  either  in  the  un- 
combined  state  or  in  union  with  carbon  as  carbonic  acid. 
Exhalation  of  Oxygen  from  Foliage,— The  relation  of 
the  haves  and  gi^een  parts  of  plants  to  oxygen  gas  has 
thus  far  been  purposely  left  unnoticed.  These  organs  like- 
wise absorb  oxygen,  and  require  its  presence  in  the  atmos- 
phere, or,  if  aquatic,  in  the  water  which  surrounds  them ; 
but  they  also,  during  their  exposure  to  Ught^  exhale  oxygen. 
This  interesting  fact  is  illusti-ated  ^paijl^ 
by  a  simple   exiDernuent.     JBill  a  lll^HiMBBf 

glass  funnel  with  any  kind  of  fresh  M^lSlil^Hf 

leaves,  and  place  it,  inverted,  in  a  ^^BBi  P^W 

wide  glass  containing  water,  fig.  ^B^^Hil^^ 

3,  so  that  it  shall  be  completely    ^afciHS'lit 
immersed,  and  displace  all  air  from   j^^^Bl^HI^^^B 
its  interior  by  agitation.    Close  the  ^^^^^^j^^^^^B 
neck  of  the  funnel    air-tight   by  lillllllfiiiliiliiliiiliire^^ 
a  cork,  and   pour   off   a    portion  ^^^'  ^• 

of  the  water  from  the  outer  vessel.  Expose  now  the 
leaves  to  strong  sunlight.  Observe  that  very  soon  minute 
bubbles  of  air  v/ill  gather  on  the  leaves.  These  will 
gradually  increase  in  size  and  detach  themselves,  and 
after  an  hour  or  two,  enough  gas  will  accumulate  in 
the  neck  of  the  funnel  to  enable  the  experimenter  to 
2 


26  HOW    CROPS    FEED. 

prove  that  it  consists  of  oxygen.  For  this  purpose  bring 
the  water  outside  the  neck  to  a  level  with  that  inside ; 
have  ready  a  splinter  of  pme,  the  end  of  which  is  glow- 
ing hot,  but  not  in  flame,  remove  the  cork,  and  insert  the 
ignited  stick  into  the  gas.  It  will  inflame  and  burn  much 
more  brightly  than  in  the  external  air.  (See  H.  C.  G.,  p. 
35,  Exp.  5.)  To  this  phenomenon,  one  of  the  most  im- 
portant connected  with  our  subject,  we  shall  recur  under 
the  head  of  carbonic  acid,  the  compound  which  is  the 
chief  source  of  this  exhaled  oxygen. 

§  3. 

RELATIONS  OF  NITROGEN   GAS   TO  VEGETABLE  NUTRITION. 

Nitrogen  Gas  not  a  Food  to  tlic  Plant. — Mtrogen  in 
the  free  state  appears  to  be  indifferent  to  vegetation. 
Priestley,  to  whom  we  are  much  indebted  for  our  knowl- 
edge of  the  atmosphere,  was  led  to  believe  in  1779  that 
free  nitrogen  is  absorbed  by  and  feeds  the  plant.  But 
this  philosopher  had  no  adequate  means  of  investigating 
the  subject.  De  Saussure,  twenty  years  later,  having 
command  of  better  methods  of  analyzing  gaseous  mix- 
tures, concluded  from  his  experiments  that  free  nitrogen 
does  not  at  all  participate  in  vegetable  nutrition. 

BoiiSSlngault'S  ExperlMClStS, — The  question  rested  un- 
til 1837,  when  Boussingault  made  some  trials,  which,  how- 
ever, were  not  decisive.  In  1851-1855  this  ingenious 
chemist  resumed  the  study  of  the  subject  and  conducted 
a  large  number  of  experiments  with  the  greatest  care, 
all  of  which  lead  to  the  conclusion  that  no  appreciable 
amount  of  free  nitrogen  is  assimilated  by  plants. 

His  plan  of  experiment  was  simply  to  cause  plants  to 
grow  in  circumstances  where,  every  other  condition  of  de- 
velopment being  supplied,  the  only  source  of  nitrogen  at 


ATMOSPHERIC    AIR   AS   THE    FOOD    OF    PLANTS.  27 

their  command,  besides  that  contained  in  the  seed  itself, 
should  be  the  free  nitrogen  of  the  atmosphere.  For  this 
purpose  he  prepared  a  soil  consisting  of  pnmice-stone  and 
the  ashes  of  stable-manure,  which  was  perfectly  freed  from 
all  compounds  of  nitrogen  by  treatment  -with  acids  and  in- 
tense heat.  In  nhie  of  his  earlier  experiments  the  soil  thus 
prepared  was  placed  at  the  bottom  of  a  large  glass  globe, 
B^  fig.  4,  of  15  to  20  gallons'  capacity.  Seeds  of  cress, 
dwarf  beans,  or  lupins,  were  deposited  in  the  soil,  and  a 
proper  supply  of  water,  purified  for  the  purpose,  was  add- 
ed. After  germination  of  the  seeds,  a  glass  globe,  D^  of 
about  one-tenth  the  capacity  of  the  larger  vessel,  was  filled 
with  carbonic  acid  (to  supply  carbon),  and  was  secured  air- 
tight to  the  mouth 
of  the  latter,  com- 
munication being 
Lad  between  them 
by  the  open  neck  at 
C.  The  apparatus 
was  then  disposed  in 
a  suitably  lighted 
place  in  a  garden, 
and  left  to  itself  for 
a  ^period  which  va- 
ried in  the  difierent 
experiments  from  \\ 
to  5  months.  At 
the  conclusion  of  the 
trial  the  plants  were 
lifted  out,  and,  to- 
^i^?-  4-  _  gether  with  the  soil 

from  which  their  roots  could  not  be  entirely  separated, 
were  subjected  to  chemical  analysis,  to  determine  the 
amount  of  nitrogen  wdiich  they  had  assimilated  during 
growth. 

The  details  of  these  trials  are  contained  in  the  subjoined 


28 


HOW    CROPS    FEED. 


Table.     The  weights  are  expressed  m  the  gram  and  its 
fractions. 


Kind  of  Plant. 


Dwarf  bean 

Oat 

Bean 

•2  mouths 

2 

3        " 

3 

Oat 

Lupin . 

2/2     " 

2 

7  weeks 

6 

u 

6        " 

Dwarf  bean  . . . 

2  months 

2/2      " 

354 

(  Cress 

J  Lupin 

as  manure 
5  months 

as  manure 

Sum. 


Duration 

of 

Exioeriment. 


^ 


'^ 


.377 
.530 
.618 
.139 
.825 
.202 
.600 
.343 
.686 
.792 
.665 
.008 
.026 
.627 
.512 


1.87 
0.54 
0.89 
1.13 
0.44 
1.82 
6.73 
1.95 
1.05 
1.53 
2.35 
2.80 

0.65 
5.76 


0.0349  0 
0.0078|0 
0.0210,0, 
0.02450, 
0.0031i0, 
0.0480J0, 
0.1282|0, 
0.0349]0 
0.0.200:0 
0.0399'0 
0.0354,0, 
0.02980, 


0340 
0067 
0189 
0226 
0030 
0483 
1246 
0339 
0204 
0397 
0360 
0277 


0.0013  0.0013 
0.182710.1697 


11 .  720    30 .  11    0 .  6135 1 0 .  5868  —0 .  0247 


11^ 


0.0009 

0.0011 

■0.0021 

0.0019 

—0.0001 

+0.0003 

-0.0036 

-0.0010 

+0.0004 

—0.0002 

+0.0006 

-0.0021 

0.0000 
—0.0130 


While  it  must  be  admitted  that  the  miavoidable  errors  of 
experiment  are  relatively  large  in  working  with  such  small 
quantities  of  material  as  Boussingault  here  employed,  we 
cannot  deny  that  the  aggregate  result  of  these  trials  is  de- 
cisive against  the  assimilation  of  free  nitrjogen,  since  there 
was  a  loss  of  nitrogen  in  the  14  experiments,  amounting 
to  4  per  cent  of  the  total  contained  in  the  seeds ;  while  a 
gain  was  indicated  in  but  3  trials,  and  was  but  0.13  per 
cent  of  the  nitrogen  concerned  in  them. — (Boussingault's 
Agronomie^  Chimie  Agricole,  et  Physiologie,  Tome  I, 
pp.  1-64.) 

The  Opposite  CoecIiisIohs  of  ¥ille, — In  the  years  1849, 
'50,  '51,  and  '52,  Georges  Ville,  at  Grenelle,  near  Paris, 
experimented  upon  the  question  of  the  assimilability  of  free 
nitrogen.  His  method  was  similar  to  that  first  employed, 
by  Boussingault.  The  plants  subjected  to  his  trials  were 
cress,  lupins,  colza,  wheat,  rye,  maize,  sun-flowers,  and  to- 
bacco. TJiey  were  situated  in  a  large  octagonal  cage 
made  of  iron  sashes,  set  with  glass-plates.     The  air  was 


ATMOSPHERIC    AIR    AS    THE    FOOD    OF    PLANTS. 


29 


constantly  renewed,  and  carbonic  acid,  was  introduced  in 
proper  quantity.  The  experiments  w^ere  conducted,  on  a 
larger  scale  than  those  of  Boussingault,  and  their  result 
was  uniformly  the  reverse.  Yille  indeed  thought  to  have 
established  that  vegetation  feeds  on  the  free  nitrogen  of 
the  air.  To  the  conclusions  to  which  Boussingault  drew 
from  the  trials  made  in  the  manner  already  described,  Ville 
objected  that  the  limited  amount  of  air  contained  in  the 
glass  globes  was  insufficient  for  the  needs  of  vegetation ; 
that  plants,  in  fact,  could  not  attain  a  normal  development 
under  the  conditions  of  Boussinganlt's  experiments. — 
(Ville,  Mecherches  sur  la  Vegetation,  pp.  29-58,  and  53-98.) 

Boussiagault's  Later  Experiments. — The  latter  there- 
upon instituted  a  new  series  of  trials  in  1854,  in  wdiich 
he  proved  that  the  plants  he  had  previously  experimented 
upon  attain  their  full  development  in  a  confined  atmosphere 
under  the  circumstances  of  his  first  experiments,  provided 
they  are  supplied  with  some  assimilable  compound  of  ni- 
trogen. He  also  conducted  seven  new  experiments  in  an 
apparatus  which  allowed  the  air  to  be  constantly  renewed, 
and  in  every  instance  confirmed  his  former  results. — 
{Agronomie,  Chimie  Agricole  et  Physiologie,  Tome  I, 
pp.  65-114.) 

The  details  of  these  experiments  are  given  in  the  follow- 
ing Table.     The  w^eights  are  expressed  in  grams. 


1 

Kind  of  Plant. 

Duration 

of 

Experiment. 

II 

S    CO 

•i 
1 

ill 

1 

9, 

Lupin 

Bean 

10  weelis 
10     " 

12  " 
14      " 

13  " 
(    9      '^ 

(  as  manure 
j  10  weelvs 
1  as  manure 

1 
1 
1 

1 
2 
1 
1 

30 
12 

0.337 

0.720 
0.748 
0.755 
1.510 

2.140 
2.000 
2.847 
2.240 
5.150 

0.0196 
0.0322 

0.0187 
0.0325 

—0.0009 
+0.0003 

S 

0.0335  0.0341 
0.0339  0.0329 

+0.0006 

4 

Bean 

-0.0010 

5 

Bean 

0.0676,0.06661—0.0010 

fi 

Lupin 

0-gn  1.730 

0.0355,0.0324—0.0021 

7 

Cress 

-  0.100 

0.533 

0.0046,0.0052+0.0006 

1     r 

Sum 

.4.780 

16.64 

0.2269 

0.2240 

-0.0035 

80  HOW    CEOPS    FEED. 

Inaccuracy  of  Yllle's  Results. — In  comparing  the  in- 
vestigations of  Boussingault  and  Ville  as  detailed  in  their 
own  words,  the  critical  reader  cannot  fail  to  be  struck 
with  the  greater  simplicity  of  the  apparatus  used  by  the 
former,  and  Lis  more  exhaustive  study  of  the  possible 
sources  of  error  incidental  to  the  investigation — facts  Avhich 
are  greatly  in  favor  of  the  conclusions  of  this  skillful  and 
experienced  philoso23her.  Furthermore  Cloez,  who  was 
employed  by  a  Commission  of  the  French  Academy  to 
oversee  the  repetition  of  Ville's  experiments,  found  that  a 
considerable  quantity  of  ammonia  was  either  generated 
within  or  introduced  into  the  apparatus  of  Yille  during 
the  period  of  the  trials,  which  of  course  vitiated  all  his 
results. 

Any  further  doubts  with  regard  to  this  important  sub- 
ject have  been  effectually  disposed  of  by  another  most 
elaborate  investigation. 

Researcli  of  Lawes^  Gilbert,  aHd  Piigh.— In  1857  and 
'58,  the  late  Dr.  Pugh,  afterward  President  of  the  Penn- 
sylvania Agricultural  College,  associated  himself  with 
Messrs.  Lawes  and  Gilbert,  of  Rothamsteacl,  England, 
for  the  purpose  of  investigating  all  those  points  con- 
nected with  the  subject,  which  the  spirited  discussion  of 
the  researches  of  Boussingault  and  Ville  had  suggested  as 
possibly  accounting  for  the  diversity  of  their  results. 
Lawes,  Gilbert,  and  Pugh,  conducted  27  experiments  on 
graminaceous  and  leguminous  plants,  and  on  buckwheat. 
The  plants  vegetated  within  large  glass  bells.  They  were 
cut  off  from  the  external  air  by  the  bells  dipping  into 
mercury.  They  were  supplied  with  renewed  portions  of 
purified  air  mixed  with  carbonic  acid,  which,  being  forced 
into  the  bells  instead  of  being  drawn  through  them,  ef- 
fectually prevented  any  ordinary  air  from  getting  access 
to  the  plants. 

To  give  an  idea  of  the  mode  in  whicli  these  delicate  investigations  are 
conducted,  we  give  here  a  figure  and  concise  description  of  the  appara- 


ATIIOSPHERIC   AIR    AS   THE    FOOD    OF    PLANTS.  31 


32  HOW  CEors  feed. 

tns  employed  lij  Lawes,  Gilbert,  and  Pugli,  in  tlieir  experiments  made  in 
the  year  1S58. 

A,  fig.  5,  represents  a  stone-ware  bottle  IS  inches  in  diameter  and  24 
inches  high. 

i?,  C,  and  U,  are  glass  3-necked  bottles  of  about  1  quart  capacity. 

^  is  a  large  glass  shade  9  inches  in  diameter  and  40  inches  high. 

a  represents  the  cross-section  of  a  leaden  pipe,  which,  passing  over  all 
the  vessels  A  of  the  series  of  16,  supplied  them  with  water,  from  a  reser- 
voir not  shown,  through  the  tube  with  stop-cock  a  b. 

c  fZ  e  is  a  leaden  exit-tube  for  air.  At  c  it  widens,  until  it  enters  the 
vessel^,  and  another  bent  tube,  q  r  s,  passes  through  it  and  reaches  to 
the  bottom  of  A,  as  indicated  by  the  dotted  lines.  The  latter  opens  at 
q,  and  serves  as  a  safety  tube  to  prevent  water  passing  into  d  e. 

The  bottles  B  C  are  partly  filled  with  strong  sulphuric  acid. 

The  tube  D  D,  1  inch  wide  and  3  feet  long,  is  filled  with  fragments  of 
pumice-stone  saturated  with  sulphuric  acid.  At//  indentations  are  made 
to  prevent  the  acid  from  draining  against  the  corks  with  which  the  tube 
is  stopped. 

The  bottle  JS  contains  a  saturated  solution  of  pure  carbonate  of  soda. 

g  7iis  a  bent  and  caoutchouc-jointed  glass  tube  connecting  the  interior 
of  the  bottle  ^  with  that  of  the  glass  shade  F. 

i  Jc,  better  indicated  in  2,  is  the  exit-tube  for  air,  connecting  the 
interior  of  the  shade  F  with  an  eight-bulbed  apparatus,  i)/,  containing 
sulphuric  acid. 

w  w  is  a  vessel  of  glazed  stone-ware,  containing  mercury  in  a  circular 
groove,  into  which  the  lower  edge  of  the  shade  F  is  dipped.  These 
glass  tubes,  g  A,  lo  v,  and  i  k,  2,  pass  under  the  edge  of  the  shade  and 
communicate  with  its  interior,  the  mercury  cutting  ofi"  all  access  of  ex- 
terior air,  except  through  the  tubes.  Another  tube,  7i  o,  passes  air-tight 
through  the  bottom  of  the  stone-ware  vessel,  and  thus  communicates 
with  its  interior. 

The  tubes  u  v  and  i  k  are  seen  best  in  2,  which  is  taken  at  right 
angles  to  1. 

The  plants  were  sprouted  and  grew  in  pots,  v,  v,-ithin  the  shades.  The 
tube  u  V  was  to  supply  them  with  water. 

The  water  which  exhaled  from  the  foliage  and  gathered  on  the  inside 
of  the  shade  ran  off  through  n  o  into  the  bottle  0.  This  water  was  re- 
turned to  the  i)ots  through  u  v. 

The  renewed  sujDply  of  pure  air  was  kept  up  through  the  bottles  and 
tube  J.,  -S,  C,  i>,  E.  On  opening  the  cock  a  6,  J.,  water  enters  J.,  and 
its  pressure  forces  air  through  the  bottles  and  tube  into  the  shade  F^ 
whence  it  finds  its  exit  through  the  tube  i  k^  and  the  bulb-apparatus  2L 
In  its  passage  through  the  strong  sulphuric  acid  of  B^  C,  and  D,  the  air 
is  completely  freed  from  ammonia,  while  the  carbonate  of  soda  of  _E^  re- 
moves any  traces  of  nitric  acid.  The  sulphuric  acid  of  the  bulb  M  puri- 
fies the  small  amount  of  air  that  might  sometimes  enter  the  shade 
through  the  tube  i  7^,  owing  to  cooling  of  the  air  in  F^  when  the  current 


ATMOSPHERIC   AIK   AS    THE    FOOD    OP    PLANTS.  33 

was  not  passing.     The  outer  ends  of  the  tubes  t  and  u  were  closed  with 
caoutchouc  tubes  and  glass  plugs. 

In  these  experiments  it  was  cons-idered  advisable  to  furnish  to  the 
plants  more  carbonic  acid  than  the  air  contains.  This  was  accomplished 
by  pouring  hydrochloric  acid  from  time  to  time  into  the  bottle  T,  which 
contained  fragments  of  marble.  The  carbonic  acid  gas  thus  liberated 
joined,  and  was  swept  on  by  the  current  of  air  in  C.  Experiments  taught 
how  much  hydrochloric  acid  to  add  and  how  often.  The  proportion  of 
this  gas  was  kept  within  the  limits  which  previous  experimenters  had 
found  permissible,  and  was  not  allowed  to  exceed  4.0  per  cent,  nor  to 
fall  below  0.3  per  cent. 

In  these  experiments  the  seeds  were  deposited  in  a  soil  purified  from 
nitrogen-compounds,  by  calcination  iu  a  current  of  air  and  subsequent 
washing  with  pure  water.  To  this  soil  was  added  about  0.5  per  cent  of 
the  ash  of  the  plant  which  was  to  grow  in  it.  The  water  used  for  wa- 
tering the  plants  was  specially  purified  from  ammonia  and  nitric  acid. 
The  experiments  of  Lawes,  Gilbert,  and  Pugh,  fully 
confirmed  those  of  Boussingault.  For  the  numerous  de- 
tails and  the  full  discussion  of  collateral  points  bearing  on 
the  study  of  this  question,  we  must  refer  to  their  elaborate 
memoir,  "  On  the  Sources  of  the  Nitrogen  of  Vegetation." 
— {Philosophical  TransaGtio7is,  1861,  II,  pp.  431-579.) 

Nitrog-en  <5as  is  aaot  E^iiiittecl  toy  JLiiviiig-  l*lamt§.— It 
was  long  supposed  by  vegetable  physiologists  that  when  the  foliage  of 
plants  is  exposed  to  the  sun,  free  nitrogen  is  evolved  by  them  in  small 
quantity.  In  fact,  when  plants  are  placed  in  the  circumstances  which 
admit  of  collecting  the  gases  that  exhale  from  them  under  the  action  of 
light,  it  is  found  that  besides  oxygen  a  quantity  of  gas  appears,  which, 
unless  special  precautions  are  observed,  consists  chiefly  of  nitrogen, 
which  was  a  part  of  the  air  that  fills  the  intercellular  spaces  of  the  plant, 
or  was  dissolved  in  the  water,  in  which,  for  the  purposes  of  experiment, 
the  plant  is  immersed. 

If,  as  Boussingault  has  recently  (1863)  done,  this  air  be  removed  from 
the  plant  and  water,  or  rather  if  its  quantity  be  accurately  determined 
and  deducted  from  that  obtained  in  the  experiment,  the  result  is  that  no 
nitrogen  gas  remains.  A  small  quantity  of  gas  besides  oxygen  was  indeed 
usually  evolved  from  the  plant  when  submerged  in  water.  The  gas  on 
examination  proved  to  be  marsh  gas. 

Cloez  was  unable  to  find  marsh  gas  in  the  air  exhaled  from  either 
aquatic  or  land  plants  submerged  in  water,  and  in  his  most  recent 
researches  (1865)  Boussingault  found  none  in  the  gases  given  off  from 
the  foliage  of  a  living  tree  examined  without  submergence. 

The  ancient  conclusion  of  Saussure,  Daubeny,  Draper,  and  others, 
that  nitrogen  is  emitted  from  the  substance  of  the  plant,  is  thus  shown 
to  have  been  based  on  an  inaccurate  method  of  investigation. 


34  HOY/    CHOPS    FEED. 

§4. 

KELATIONS  OF  ATMOSPHERIC  WATER  TO  VEGETABLE 
NUTRITION. 

Occiirreace  of  Water  in  the  Atmospliere. — If  water  be 
exposed  to  the  air  in  a  shallow,  open  vessel  for  some  time, 
it  is  seen  to  decrease  in  quantity,  and  finally  disappears  en- 
tirely ;  it  evaporates,  vaporizes,  or  volatilizes.  It  is  con- 
verted into  vapor.  It  assumes  the  form  of  air,  and  becomes 
a  part  of  the  atmospliere. 

The  rapidity  of  evaporation  is  greater  the  more  eleva- 
ted the  temperature  of  the  water,  and  the  drier  the  atmos- 
phere that  is  over  it.  Even  snow  and  ice  slowly  suffer 
loss  of  weight  in  a  dry  day  though  it  be  frosty. 

In  this  manner  evaporation  is  almost  constantly  going 
on  from  the  surface  of  the  ocean  and  all  other  bodies  of 
water,  so  that  the  air  always  carries  a  portion  of  aqueous 
vapor. 

On  the  other  hand,  a  body  or  mixture  whose  tempera- 
ture is  far  lower  than  that  of  the  atmosphere,  condenses 
vapor  from  the  au'  and  makes  it  manifest  in  the  form  of 
water.  Thus  a  glass  of  ice- water  in  a  warm  summer's  day 
becomes  externally  bedewed  with  moisture.  In  a  similar 
manner,  dew  deposits  in  clear  and  calm  summer  nights 
upon  the  surface  of  the  ground,  upon  grass,  and  upon  all 
exposed  objects,  whose  temperature  rapidly  falls  when 
they  cease  to  be  warmed  by  the  sun.  Again,  when  the 
invisible  vapor  which  fills  a  hot  tea-kettle  or  steam-boiler 
issues  into  cold  air,  a  visible  cloud  is  immediately  formed, 
which  consists  of  minute  droplets  of  water.  In  like  man- 
ner, fogs  and  the  clouds  of  the  sky  are  produced  by  the 
cooling  of  air  charged  with  vapor.  When  the  cooling  is 
sufficiently  great  and  sudden,  the  droplets  acquire  such 
size  as  to  fall  directly  to  the  ground ;  the  water  assumes 
the  form  of  rain. 


ATMOSPHERIC    AIll    AS    THE   FOOD    OF    PLANTS.  35 

Water  then  exists  in  the  atmosphere  during  the  periods 
of  vegetable  activity  as  gas  or  vapor,*  and  as  liquid.  In 
the  former  state  it  is  almost  perpetually  rising  into  the  air, 
while  in  the  latter  form  it  frequently  falls  again  to  the 
ground.  It  is  thus  in  a  continual  transition,  back  and 
forth,  from  the  earth  to  the  sky,  and  from  the  sky  to  the 
earth. 

We  have  given  the  average  quantity  of  water-vapor  in 
the  air  at  one  per  cent ;  but  the  amount  is  very  variable, 
and  is  almost  constantly  fluctuating.  It  may  range  from 
less  than  one-half  to  two  and  a  half  or  three  per  cent,  ac- 
cording to  temperature  and  other  circumstances. 

When  the  air  is  damp,  it  is  saturated  with  moisture,  so 
that  water  is  readily  deposited  upon  cool  objects.  On  the 
other  hand,  when  dry,  it  is  capable  of  taking  np  additional 
moisture,  and  thus  facilitates  evaporation. 

Is  Atmospheric  Water  Absorbed  by  Plants] — It  has 

long  been  supposed  that  growing  vegetation  has  the  power 
to  absorb  vapor  of  water  from  the  atmosphere  by  its 
foliage,  as  well  as  to  imbibe  the  liquid  water  which  in  the 
form  of  rain  and  dew  may  come  in  contact  with  its  leaves. 
Experiments  which  have  been  instituted  for  the  purpose 
of  ascertaining  the  exact  state  of  this  question  have,  how- 
ever, demonstrated  that  agricultural  plants  gather  little  or 
no  water  from  these  sources. 

The  wilting  of  a  plant  results  from  the  fact  that  the 
leaves  suffer  water  to  evaporate  from  them  more  rapidly 
than  the  roots  can  take  it  np.  The  speedy  reviving  of  a 
wilted  plant  on  the  falling  of  a  sudden  rain  or  on  the  depo- 
sition of  dew  depends,  not  so  much  on  the  absorption  by 
the  foliage,  of  the  water  that  gathers  on  it,  as  it  does 


*  While  there  is  properly  no  essential  difference  between  a  gas  and  a  vapor, 
the  former  term  is  commonly  applied  more  especially  to  aeriform  bodies  which 
are  not  readily  brought  to  the  liquid  state,  and  the  latter  to  those  which  are  easily 
condensed  to  liquids  or  solids. 


36  HOW    CROPS    FEED. 

on  the  suppression  of  evaporation,  which  is  a  consequence 
of  the  saturation  of  the  surrounding  air  with  water. 

linger,  and  more  recently  Duchartre,  have  found,  1st, 
that  plants  lose  weight  (from  loss  of  water)  in  air  that  is 
as  nearly  as  possible  saturated  with  vapor,  when  their 
roots  are  not  in  contact  with  soil  or  liquid  water.  Du- 
chartre has  shown,  2d,  that  plants  do  not  gain,  but  some- 
times lose  weight  when  their  foliage  only  is  exposed  to 
dew  or  even  to  rain  continued  through  eighteen  hours,  al- 
though they  increase  in  weight  strikingly  (from  absorption 
of  water  through  their  roots,)  v/hen  the  rain  is  allowed  to 
fall  upon  the  soil  in  which  they  are  planted. 

Knop  has  shown,  on  the  other  hand,  that  leaves,  either 
separate  or  attached  to  twigs,  gain  weight  by  continued 
immersion  in  water,  and  not  only  recover  what  they  may 
have  lost  by  exposure,  but  absorb  more  than  they  orig- 
inally contained.     {Yersuchs-8tatlonen^  YI,  252.) 

The  water  of  dews  and  rains,  it  must  be  remembered, 
however,  does  not  often  thoroughly  wet  the  absorbent  sur- 
face of  the  leaves  of  most  plants;  its  contact  being  pre- 
vented, to  a  great  degree,  by  the  hairs  or  wax  of  the 
epidermis. 

Finally,  3d,  Sachs  has  found  that  even  the  roots  of 
plants  appear  incapable  of  taking  up  watery  vapor. 

To  convey  an  idea  of  the  method  employed  in  such 
investigations,  we  may  quote  Sachs'  account  of  one 
of  his  experiments.  (  K  St.^  II,  7.)  A  young  camellia, 
having  several  fresh  leaves,  was  taken  from  the  loose 
soil  of  the  pot  in  which  it  had  been  growing ;  from 
its  long  roots  all  particles  of  earth  were  carefully  remov- 
ed, and  its  weight  was  ascertained.  The  bottom  of  a 
glass  cylinder  was  covered  with  water  to  a  little  depth, 
and  the  roots  of  the  camellia  were  introduced,  but  not  in 
contact  with  the  water.     The  stem  was  supported  at  its 


ATMOSPHEEIC    AIE    AS    THE    FOOD    OF    PLANTS.  37 

lower  part  in  a  hole  in  a  glass  cover,*  that  was  cemented 
air-tight  upon  the  vessel.  The  stem  itself  was  cemented 
by  soft  wax  into  the  hole,  so  that  the  interior  of  the  ves- 
sel was  completely  cut  off  from  direct  communication  with 
the  external  atmosphere.  The  plant  thus  situated  had  its 
roots  in  an  atmosphere  as  nearly  as  possible  saturated  with 
vapor  of  water,  while  its  leaves  were  exposed  to  the  ex- 
ternal air.  After  four  days  had  expired,  the  entire  appa- 
ratus, plant  included,  had  lost  1.823  grm.  Thereupon  the 
plant  was  removed  from  the  vessel  and  weighed  by  itself; 
it  had  lost  2.188  grm.  The  loss  of  the  entire  apparatus 
was  due  to  vapor  of  water,  which  had  escaped  through 
the  leaves.  The  difference  between  this  loss  and  the  loss 
which  the  plant  had  experienced  could  be  attributed  only 
to  an  exhalation  of  water  through  the  roots,  and  amount- 
ed to  (2.188  —  1.823=)  0.365  grm. 

This  exhalation  of  water  into  the  confined  and  moist  at- 
mosphere of  the  glass  vessel  is  explained,  according  to 
Sachs,  by  the  fact  that  the  chemical  changes  proceeding 
within  the  plant  elevate  its  temperature  above  that  of  the 
surrounding  atmosphere. 

Knop,  in  experiments  on  the  transpiration  of  plants, 
(FT  JSt.,  VI,  255,)  obtained  similar  results.  He  found, 
however,  that  a  moist  piece  of  paper  or  wood  also  lost 
weight  when  kept  for  some  time  in  a  confined  space  over 
water.  He  therefore  concludes  that  it  is  nearly  impossible  in 
the  conditions  of  such  experiments  to  maintain  the  air  sat- 
urated with  vapor,  and  that  the  loss  of  weight  by  the  roots 
is  due,  not  to  the  heat  arising  from  internal  chemical 
changes,  but  to  simple  evaporation  from  their  surface.  In 
one  instance  he  found  that  a  portulacca  standing  over 
night  in  a  bell-glass  with  moistened  sides,  did  not  lose,  but 
gained  weight,  some  dew  having  gathered  on  its  foliage. 


*  The  cover  consisted  of  two  semicircular  pieces  of  ground  glass,  each  of 
which  had  a  small  semicircular  notch,  so  that  the  two  could  be  brought  together 
by  their  straight  edges  around  the  stem. 


DO  HOW    CROPS    FEED. 

The  result  of  these  investigations  is,  that  while,  perhaps, 
wilted  foliage  in  a  heavy  rain  may  take  up  a  small  quan- 
tity of  water,  and  while  foliage  and  roots  may  absorb 
some  vapor,  yet  in  general  and  for  the  most  part  the  at- 
mospheric water  is  not  directly  taken  up  to  any  great  ex- 
tent by  plants,  and  does  not  therefore  contribute  immedi- 
ately to  their  nourishment. 

Atmosplieric  Water  Enters  Crops  through  the  Soil. — 

It  is  only  after  the  water  of  the  atmosphere  has  become  in- 
corporated with  the  soil,  that  it  enters  freely  into  agricul- 
tural plants.  The  relations  of  this  substance  to  proper 
vegetable  nutrition  may  then  be  most  appropriately  dis- 
cussed in  detail  v/hen  we  come  to  consider  the  soil.  (See 
p.  199.) 

It  is  probable  that  certain  air-plants  (epiphytes)  native  to  the  tropics, 
which  have  no  connection  with  the  soil,  and  are  not  rooted  in  a  medium 
capable  of  j-ielding  water,  condense  yapor  from  the  air  in  considerable 
quantity.  So  also  it  is  proved  that  the  mosses  and  lichens  absorb  water 
largely  from  moist  air,  and  it  is  well  known  that  they  become  dry  and 
brittle  in  hot  weather,  recovering  their  freshness  and  flexibility  when  the 
air  is  damp. 

§5. 

RELATIONS  OF  CARBONIC  ACID  GAS  TO  VEGETABLE 
NUTRITION. 

Compositioa  and  Properties  of  Carhoaic   Acid,  — 

When  12  grains  of  j^ure  carbon  are  heated  to  redness 
in  32  grains  of  pure  oxygen  gas,  the  two  bodies  unite  to- 
gether, themselves  completely  disappearing,  and  44  grains 
of  a  gas  are  produced  which  has  the  same  bulk  as  the 
oxygen  had  at  the  beginning  of  the  experiment.  The  new 
gas  is  nearly  one-half  heavier  than  oxygen,  and  differs  in 
most  of  its  properties  from  both  of  its  ingredients.  It  is 
carbonic  acid.  This  substance  is  the  product  of  the  burn- 
ing of  charcoal  in  oxygen  gas,  (H.  C.  G.,  p.  35,  Exj^.  6.) 
It  is,  in  fact,  produced  whenever  any  organic  body  is 


ATMOSPHERIC    AIR    AS    THE    FOOD    OF    PLANTS,  39 

burned  or  decays  in  contact  with  the  air.  It  is  like  oxy- 
gen, colorless,  but  it  has  a  peculiar  pungent  odor  and 
pleasant  acid  taste. 

The  composition  of  carbonic  acid  is  evident  from  what 
has  been  said  as  to  its  production  from  carbon  and  oxygen. 
It  consists  of  two  atoms,  or  32  parts  by  weight,  of  oxygen, 
united  to  one  atom,  or  12  parts,  of  carbon.  Its  symbol  is 
CO^.  In  the  subjoined  scheme  are  given  its  symbolic, 
atomic,  and  percentage  composition. 


At.  wL 

Per  cent. 

c 

=      12 

27.27 

0, 

=      32 

72.73 

CO2      =      4A  100.00 

In  a  state  of  combination  carbonic  acid  exists  in  nature 
in  immense  quantities.  Limestone,  marble,  and  chalk, 
contain,  when  pure,  44  per  cent  of  this  acid  united  to  lime. 
These  minerals  are  in  chemical  language  carbonate  of  lime. 
Common  salseratus  is  a  carbonate  of  potash,  and  soda- 
salseratus  is  a  carbonate  of  soda. 

From  either  of  these  carbonates  it  is  easy  to  separate 
this  gas  by  the  addition  of  another  and  stronger  acid. 

For  this  purpose  we  may  employ  the  Eochelle  or  Seidlitz  powders  so 
commonly  used  in  medicine.  If  we  mingle  together  in  the  dry  state  the 
contents  of  a  blue  paper,  which  contains  carbonate  of  soda,  with  those  of 
a  white  paper,  which  consist  of  tartaric  acid,  nothing  is  observed.  If, 
however,  the  mixture  be  placed  at  the  bottom  of  a  tall  bottle,  and  a  little 
water  be  poured  upon  it,  at  once  a  vigorous  bubbling  sets  in,  which  is 
caused  by  the  liberated  carbonic  acid.* 

Some  important  properties  of  the  gas  thus  set  free  may  be  readily 
made  manifest  by  the  following  experiments. 

a.  If  a  burning  taper  or  match  be  immersed  in  the  gas,  the  flame  is 
immediately  extinguished.  This  happens  because  of  the  absence  of  free 
oxygen. 

h.  If  the  mouth  of  the  bottle  from  which  carbonic  acid  is  escaj)ing  be 
held  to  that  of  another  bottle,  the  gas  can  be  poured  into  the  second  ves- 
sel, on  account  of  its  densit}^  being  one-half  greater  than  that  of  the  air. 
Proof  that  the  invisible  gas  has  thus  been  transferred  is  had  by  placing 


*  Chalk,  marble,  or  salseratus,  and  chlorhydric  (muriatic)  acid,  or  strong  vine- 
gar (acetic  acid)  can  be  equally  well  employed. 


40  HOW    CROPS    FEED. 

a  burning  taper  in  tbe  second  bottle,  when,  if  the  experiment  was  right- 
1}'  conducted,  the  flame  will  be  extinguished. 

c.  Into  a  bottle  filled  as  in  the  last  experiment  with  carbonic  acid, 
some  lime-water  is  poured  and  agitated.  The  previously  clear  lime-wa- 
ter immediately  becomes  turbid  and  milky  from  the  formation  of  carbon- 
ate of  lime^  which  is  nearly  insoluble  in  water. 

CarboMlc  Acid  in  tlie  Atmosphere. — To  show  the  pres- 
ence of  carbonic  acid  in  the  atmosjjhere,  it  is  only  neces- 
sary to  expose  lime-water  in  an  open  vessel.  But  a  little 
time  elapses  before  the  liquid  is  covered  with  a  white  film 
of  carbonate.  As  already  stated,  the  average  proportion 
of  carbonic  acid  in  the  atmosphere  is  6-lOOOOths 
(l-1600th  nearly)  by  weight,  or  4-lOOOOths  (l-2500th) 
by  bulk.  Its  quantity  varies  somewhat,  however.  Among 
over  300  analyses  made  by  De  Saussure  in  Switzerland, 
Yerver  in  Holland,  Lewy  in  E'ew  Granada,  and  Gilm  in 
Austria,  the  extreme  range  was  from  47  to  86  parts  by 
weight  in  100,000. 

DeportmeMt  of  Carfeosslc  Add  towards  Water, — Water 
dissolves  carbonic  acid  to  a  greater  or  less  extent,  accord- 
ing to  the  temperature  and  pressure.  Under  the  best  or- 
dinary conditions  it  takes  up  about  its  own  volume  of  the 
gas.  At  the  freezing  point  it  may  absorb  nearly  twice  as 
much.  This  gas  is  therefore  usually  found  in  spring,  well, 
and  river  waters,  as  well  as  in  dew  and  rain.  The  consid- 
erable amount  held  in  solution  in  cold  springs  and  wells 
is  a  principal  reason  of  the  refreshing  quality  of  their  wa- 
ter. Under  pressure  the  proportion  of  carbonic  acid  ab- 
sorbed by  water  is  much  larger,  and  when  the  pressure  is 
removed,  a  portion  of  the  gas  escapes,  resuming  its  gase- 
ous form  and  causing  effervescence.  The  liquid  that  flows 
from  a  soda-fountain  is  an  aqueous  solution  of  carbonic 
acid,  made  under  pressure.  Bottled  cider,  ale,  champagne, 
and  all  effervescent  beverages,  owe  their  sparkle  and  much 
of  their  refreshing  qualities  to  the  carbonic  acid  they  con- 
tain. 


ATMOSPHERIC    AIIl    AS    THE    FOOD    OF    PLAIS'TS.  41 

.  Tiie  ll>sorptl©ii  of  CariMnic  Acid  fey  Plants. — In  1771 
Priestley,  in  England,  found  that  the  leaves  of  plants  im- 
mersed in  water,  sometimes  disengaged  carbonic  acid, 
sometimes  oxygen,  and  sometimes  no  gas  at  all.  A  few 
years  later  Ingenhouss  proved  that  the  exhalation  of  car- 
bonic acid  takes  place  in  the  absence,  and  that  of  oxygen 
in  the  presence,  of  solar  light.  Several  years  more  elapsed 
before  Sennebier  first  demonstrated  that  the  oxygen  which 
is  exhaled  by  foliage  in  the  sunlight  comes  from  the  car- 
bonic acid  contained  in  the  water  in  v/hicli  the  plants  are 
immersed  for  the  purpose  of  these  experiments.  It  had 
been  already  noticed,  by  Ingenhouss,  that  in  spring  water 
plants  evolve  more  oxygen  than  in  river  water.  We  now 
know  that  the  former  contains  more  carbonic  acid  than  the 
latter.  Where  the  water  is  by  accident  or  purposely  free 
from  carbonic  acid,  no  gas  is  evolved  by  foliage  in  the 
sunlight. 

The  attention  of  scientiiic  men  was  greatly  attracted 
by  these  interesting  discoveries  ;  and  shortly  Percival,  in 
England,  found  that  a  plant  of  mint  whose  roots  Avere 
stationed  in  water,  flourished  better  when  the  air  bathing 
its  foliage  was  artificially  enriched  in  carbonic  acid  than  in 
the  ordinary  atmosphere. 

In  1840  Boussingauit  furnished  direct  proof,  of  what 

indeed  was  hardly  to  be  doubted,  viz.:  the  absorption  of 

the  carbonic  acid  of  the  atmosphere  by  foliage. 

Into  one  of  the  orifices  in  a  three-neclied  glass  globe  lie  introduced 
and  fixed  air-tight  the  branch  of  a  living  vine  bearing  twenty  leaves ; 
vrith  another  opening  he  connected  a  tube  through  which  a  slow  current 
of  air,  containing,  in  one  experiment,  four-lOOOOths  of  carbonic  acid, 
could  be  i^assed  into  the  globe.  This  air  after  streaming  over  the  vine 
leaves,  at  the  rate  of  about  15  gallons  per  hour,  escaped  by  the  third 
neck  iuto  an  arrangement  for  collecting  and  weighing  the  carbonic  acid 
that  remained  in  it.  The  experiment  being  set  in  process  in  the  sun- 
light, it  was  found  that  the  enclosed  foliage  removed  from  the  current 
of  air  three-fourths  of  the  carbonic  acid  it  at  first  contained. 

Influence  of  the  Helative  Quantity  of  Carfeonk  AcM.— 
De  Saussure  investigated  the  influence  of  various  proper- 


42  HOY/    CEOPS    FEED. 

tions  of  carbonic  acid  mixed  with  atmosplieric  air  on  the 
development  of  vegetation.  He  found  that  young  peas  (4 
inches  high)  when  exposed  to  direct  sunlight,  endured  for 
some  days  an  atmosphere  consisting  to  one-half  of  carbonic 
acid.  When  the  proportion  of  this  gas  was  increased  to 
two-thirds  or  more,  they  speedily  withered.  In  air  con- 
taining one-twelfth  of  carbonic  acid  the  peas  flourished 
much  better  than  in  ordinary  atmospheric  air.  The  aver- 
age increase  of  each  of  the  plants  exposed  to  the  latter 
for  five  or  six  hours  daily  during  ten  days  was  eight 
grains  ;  w^hile  in  the  former  it  amounted  in  the  same  time  to 
eleven  grains.  In  the  shade,  however,  Saussure  found  that 
increase  of  the  proportion  of  carbonic  acid  to  one-twelfth 
was  detrimental  to  the  plants.  Their  growth  under  these 
circumstances  was  but  three-fifths  of  that  experienced  by 
similar  plants  exposed  to  the  same  light  for  the  same  time, 
but  in  common  air.  He  also  proved  that  foliage  cannot  long 
exist  in  the  total  absence  of  carbonic  acid,  when  exposed 
to  direct  sunlight.  .  This  result  was  obtained  by  enclosing 
young  plants  whose  roots  were  immersed  in  water,  or  the 
branches  of  trees  stationed  in  the  soil,  in  a  vessel  which 
contained  moistened  quicklime.  This  substance  rapidly 
absorbs  and  fixes  carbonic  acid,  forming  carbonate  of  lime. 
Thus  situated,  the  leaves  began  in  a  few  days  to  turn  yel- 
low, and  in  two  to  three  weeks  they  dropped  ofil 

In  darkness  the  presence  of  lime  not  only  did  not  de- 
stroy the  plants,  but  they  prospered  the  better  for  its 
presence,  i.  e.,  for  the  absence  or  constant  removal  of  car- 
bonic acid. 

Boussingault  has  lately  shown  that  pure  carbonic  acid 
is  decomposed  by  leaves  exposed  to  sunlight  with  extreme 
slowness,  or  not  at  all.  It  must  be  mixed  with  some  other 
gas,  and  when  diluted  -with  either  oxygen,  nitrogen,  or  hy- 
drogen, or  even  v/hen  rarefied  by  the  air-pump  to  a  certain 
extent,  the  absorption  and  decomposition  proceed  as  usual. 

ConclusiOH, — It  thus  is  proved   Ist,  that  vegetation 


ATMOSPHERIC    AIR    AS    THE    FOOD    OF    PLANTS.  4o 

can  flourisli  only  when  its  foliage  is  bathed  by  an  atmos- 
phere which  contains  a  certain  small  amount  of  carbonic 
acid ;  2d,  that  this  gas  is  absorbed  by  the  leaves,  and,  un- 
der the  influence  of  sunlight,  is  decomposed  within  the 
plant,  its  carbon  being  retained,  and  in  an  unknown  man- 
ner becoming  a  part  of  the  plant  itself,  Avhile  the  oxygen 
is  exhaled  into  the  atmosphere  in  the  free  state. 

Relative  voliimes  of  absorbed  Carbonic  Add  and  ex- 
haled Oxygen, — From  the  numerous  experiments  of  T>e 
Saussure,  and  from  similar  ones  made  recently  with  greatly 
improved  means  of  research  by  linger  and  Knop,  it  is  es- 
tablished that  in  sunlight  the  volume  of  oxygen  exhaled 
is  nearly  equal  to  the  volume  of  carbonic  acid  absorbed. 
Since  free  oxygen  occupies  the  same  bulk  as  the  carbonic 
acid  produced  by  uniting  it  with  carbon,  it  is  evident  that 
carbon  mainly  and  not  oxygen  to  much  extent,  is  retained 
by  the  plant  from  this  source. 

Hespiration  and  Fixation  ©f  Carbon  by  Plants,— In 
1851  Garreau,  and  in  1858  Corenwinder,  reviewed  experi- 
mentally the  whole  subject  of  the  relations  of  plants  to 
carbonic  acid.  Their  researches  fully  confirm  the  conclu- 
sions derived  from  older  investigations,  and  furnish  some 
additional  facts. 

We  have  already  seen  (p.  22)  that  the  plant  requires 
free  oxygen,  and  that  this  gas  is  absorbed  by  those  parts 
of  vegetation  which  are  in  the  act  of  growth.  As  a  con- 
sequence of  this  entrance  of  oxygen  into  the  plant,  a  cor- 
responding amount  of  carbonic  acid  is  produced  within 
and  exhales  from  it.  There  go  on  accordingly,  in  the  ex- 
panding plant,  two  opposite  processes,  viz.,  the  absorption 
of  oxygen  and  exhalation  of  carbonic  acid,  and  the  ab- 
sorption of  carbonic  acid  and  evolution  of  oxygen.  The 
first  process  is  chemically  analogous  with  the  breathing 
of  animals,  and  may  hence  be  designated  as  respiration. 
We  may  speak  of  the  other  process  as  the  fixation  of 
carbon. 


44  HOVv'    CROPS    FEED. 

These  opposite  changes  obviously  cannot  take  place  at 
the  same  points,  but  must  proceed  in  different  organs  or 
cells,  or  in  different  parts  of  the  same  cells.  They  further- 
more tend  to  counterbalance  each  other  m  their  effects  on 
the  atmosphere  surrounding  the  plant.  The  processes  to 
which  the  absorption  of  oxygen  and.  evolution  of  carbonic 
acid  are  necessary,  appear  to  go  on  at  all  hours  of  the  day 
and  night,  and  to  be  independent  of  the  solar  liglit.  The 
production  of  carbonic  acid  is  then  continually  occurring ; 
but,  under  the  influence  of  the  sun's  direct  rays,  the  oppo- 
site absorption  of  carbonic  acid  and  evolution  of  oxygen 
proceed  so  much  more  rapidly,  that  when  we  experiment 
with  the  entire  plant  the  first  result  is  completely  masked. 
In  our  experiments  we  can,  in  fact,  only  measure  the  pre- 
ponderance of  the  latter  process  over  the  former.  In  sun- 
light it  may  easily  happen  that  the  carbonic  acid  which 
exhales  from  one  cell  is  instantly  absorbed  by  another,  and 
likewise  the  oxygen,  which  escapes  from  the  latter,  may 
be  in  part  imbibed  by  the  former. 

In  total  darkness  it  is  believed  that  carbonic  acid  is  not 
absorbed  and  decomposed  by  the  plant,  but  only  produced 
in,  and  exhaled  from  it.  In  no  case  has  any  evolution  of 
oxygen  been  observed  in  the  absence  of  light. 

When,  instead  of  being  exposed  to  the  direct  rays  of 
the  sun,  only  the  diffused  light  of  cloudy  days  or  the  soft- 
ened light  of  a  dense  forest  acts  upon  them,  plants  may,  ac- 
cording to  circumstances,  exhale  either  oxygen  or  carbonic 
acid  in  preponderating  quantity.  In  his  earlier  investiga- 
tions, Corenwinder  observed  an  exhalation  of  carbonic  acid 
in  diffused  light  in  the  cases  of  tobacco,  sunflower,  lupine, 
cabbage,  and  nettle.  On  the  contrary,  he  found  that  let- 
tuce, the  pea,  violet,  fuchsia,  periwinkle,  and  others,  evolv- 
ed oxygen  under  similar  conditions.  In  one  instance  a 
bean  exhaled  neither  gas.  These  differences  are  not  pe- 
culiar to  the  plants  just  specified,  but  depend  upon  the  in- 
tensity of  the  light  and  the  stage  of  development  in  which 


ATMOSPHEEIC    AIR    AS    THE    FOOD    OP    PLANTS.  45 

the  j^lant  exists.  Corenwinder  noticed  that  the  evolution 
of  carbonic  acid  in  diffused  light  was  best  exhibited  by 
very  young  plants,  and  mostly  ceased  as  they  grew  older. 

Corenwinder  has  confirmed  and  extended  these  observa- 
tions in  more  recent  investigations.  {Ann.  d.  8oi.  JVat., 
1864,  I,  297.) 

He  finds  that  buds  and  young  leaves  exhale  carbonic 
acid  (and  absorb  oxygen)  by  day,  even  in  bright  sunshine. 
He  also  finds  that  all  leaves  exhale  carbonic  acid  not  alone 
at  night,  but  likewise  by  day,  when  placed  in  the  diffused 
light  of  a  room,  illuminated  from  only  one  side.  A  plant, 
which  in  full  light  yields  no  carbonic  acid  to  a  slow  stream 
of  air  passing  its  foliage,  immediately  gives  off  the  gas 
when  carried  into  such  an  apartment,  and  vice  versa. 

Amount  of  Carfeoiik  Acid  al)Sorl)€d. — The  quantity  of 
carbonic  acid  absorbed  by  day  in  direct  light  is  vastly 
greater  than  that  exhaled  during  the  night.  According 
10  Corenwinder's  experiments,  15  to  20  minutes  of  direct 
sunlight  enable  colza,  the  pea,  the  raspberry,  the  bean, 
and  sunflower,  to  absorb  as  much  carbonic  acid  as  they 
exhale  during  a  whole  night. 

As  to  the  amount  of  carbonic  acid  whose  carbon  is  re- 
tained, Corenwinder  found  that  a  single  colza  plant  took 
up  in  one  day  of  strong  sunshine  more  than  two  quarts  of 
the  gas. 

Boussingault  {Comptes  Rend.^  Oct.  23d,  1865)  found  as 
the  average  of  a  number  of  experiments,  that  a  square  me- 
ter of  oleander  leaves  decomposed  in  sunlight  1.108  liters 
of  carbonic  acid  per  hour.  In  the  dark,  the  same  surface 
of  leaf  exhaled  but  0.07  liter  of  this  gas. 

Composition  of  the  Air  within  the  Plant, — Full  con- 
firmation of  the  statements  above  made  is  furnished  by 
tracing  the  changes  which  take  place  w^ithin  the  vegeta- 
ble tissues.  Lawes,  Gilbert,  and  Pugh,  (Phil.  Trans.., 
1861,  II,  p.  486,)  have  examined  the  composition  of  the 


46 


Plow    CROPS    FEED. 


air  contained  in  plants,  as  well  when  the  latter  are  remov- 
ed from,  as  Avhen  they  are  subjected  to,  the  action  of  light. 
To  collect  the  gas  from  the  plants,  the  latter  were  placed 
in  a  glass  vessel  filled  with  water,  from  which  all  air  had 
been  expelled  by  long  boiling  and  subsequent  cooling  in 
full  and  tightly  closed  bottles.  The  vessel  was  then  con- 
nected with  a  simple  apparatus  in  which  a  vacuum  was 
produced  by  the  fall  of  mercury,  down  a  tube  of  80  inches 
height.  The  air  contained  within  the  cells  of  the  plant 
was  thus  drawn  over  into  the  vacuum  and  collected  for 
examination.  We  give  some  of  the  results  of  the  6th 
series  of  their  examinations.  "  The  Table  shows  the 
Amount  and  Composition  of  the  Gas  evolved  into  a  Tor- 
ricellian vacuum  by  duplicate  portions  of  oat-plant,  both 
kept  in  the  dark  for  some  time,  and  then  one  exposed  to 
sunlight  for  about  twenty  minutes,  when  both  were  sub- 
mitted to  exhaustion." 

T?er  cent. 


Date, 

1858. 


Conditions 

during 
Exhausiion. 


Cubic  centimeters 

of 

Gas  collected. 


Nitrogen. 


Oxygen. 


Carbonic  Acid. 


July  31. 
Aug.  2. 
Aug.   2. 


j  In  dark. 
j  In  sunlight, 
j  In  dark. 
(  In  sunlight. 
J  In  dark. 
1 1n  sunlight. 


24.0 
34.5 
10.6 
39.2 
30.7 
26.5 


77.08 
68.69 
68.28 
67.86 
76.87 
69.43 


3.75 
24.93 
10.21 
25.95 

8.14 
27.17 


19.17 
6.38 

21.51 
6.89 

14.99 
3.40 


These  analyses  show  plainly  what  it  is  that  haj)pens  in 
the  cells  of  the  plant.  The  atmospheric  air  freely  j^ene- 
trates  the  vegetable  tissues,  (H.  C,  G.,  p.  288.)  In  dark- 
ness, the  oxygen  that  is  thus  contained  within  the  plant 
takes  carbon  from  the  vegetable  matter  and  forms  with  it 
carbonic  acid.  This  j^rocess  goes  on  with  comparative 
rapidity,  and  the  proportion  of  oxygen  may  be  diminish- 
ed from  21,  the  normal  percentage,  to  4,  or  even,  as  in 
some  other  experiments,  to  less  than  1  per  cent  of  the 
volume  of  the  air.  Upon  bringing  the  vegetable  tissue 
into  sunlight,  the  carbonic  acid  previously  formed  within 
the  cells  undergoes  decomposition,  with  se"paration  of  its 


ATMOSPHERIC    AIR    AS    THE    FOOD    OF    PLANTS.  47 

oxygen  in  the  free  gaseous  condition,  while  its  carbon  re- 
mains in  the  solid  state  as  a  constituent  of  the  plant.  Re- 
ferring to  the  table  above,  we  see  that  twenty  minutes' 
exposure  to  the  solar  rays  was  sufficient  in  the  second  ex- 
periment (where  the  proportion  of  nitrogen  remained 
nearly  unaltered)  to  decompose  14  per  cent  of  carbonic  acid 
and  liberate  its  oxygen.  The  total  volume  of  air  collected 
was  2.4  cubic  inches,  and  the  volume  of  decomposed  car- 
bonic acid  was  ^  of  a  cubic  inch,  that  of  the  liberated 
oxygen  being  the  same. 

Supply  of  Carbonic  Acid  ia  the  Atmospiiere.— Although 
this  body  forms  but  loooo  of  the  weight  of  the  atmosphere, 
yet  such  is  the  immense  volume  of  the  latter  that  it  is  cal- 
culated to  contain,  when  taken  to  its  entire  height,  no  less 
than  3,400,000,000,000  tons  of  carbonic  acid.  This 
amounts  to  about  28  tons  over  every  acre  of  the  earth's 
surface. 

According  to  Chevandier,  an  acre  of  beech-forest  annu- 
ally assimilates  about  one  ton  (1950  lbs.)  of  carbon,  an 
amount  equivalent  to  3|-  tons  of  this  gas.  Were  the  whole 
earth  covered  with  this  kind  of  forest,  and  did  it  depend 
solely  upon  the  atmosphere  for  carbon,  eight  years  must 
elapse  before  the  existing  supply  would  be  exhausted,  in 
case  no  means  had  been  provided  for  restoring  to  the  air 
what  vegetation  constantly  removes. 

When  we  consider  that  but  one-fourtb  of  the  earth's 
surface  is  land,  and  that  on  this  the  annual  vegetable  pro- 
duction is  very  far  below  (not  one-third)  the  amount  stat- 
ed above  for  thrifty  forest,  we  are  warranted  in  assuming 
the  atmospheric  content  of  carbonic  acid  sufficient,  with- 
out renewal,  for  a  hundred  years  of  growth.  This  ingredi- 
ent of  the  atmosphere  is  maintained  in  undiminished 
quantity  by  the  oxidation  of  carbon  in  the  slow  decay  of 
organic  matters,  in  the  combustion  of  fuel,  and  in  animal 
respiration. 

That  the  carbonic  acid  of  the  atmosphere  may  fully  suf- 


48  HOW    CROPS    FEED 

iice  to  provide  a  rapidly  growing  vegetation  with  carbon 
is  demonstrated  by  numerous  facts.  Here  w^e  need  only 
mention  that  in  a  soil  totally  destitute  of  all  carbon,  be- 
sides that  contained  in  the  seeds  sown  in  it,  Boussingault 
brought  sunflowers  to  a  normal  development.  The  writer 
has  done  the  same  with  buckwheat;  and  Sachs,  Knop, 
Stohmann,  Kobbe  and  Siegert,  and  others,  have  produced 
perfect  plants  of  maize,  oats,  etc.,  whose  roots,  throughout 
the  whole  period  of  growth,  were  immersed  in  a  weak, 
saliue  solution,  destitute  of  carbon.  (See  H.  C.  G.,  Water 
Culture,  p.  167.) 

Hellriegel's  recent  experiments  give  the  result  that  the 
atmospheric  supply  of  carbonic  acid  is  probably  sufficient 
for  the  production  of  a  maximum  crop  under  all  circum- 
stances ;  at  least  artificial  supply,  whether  of  the  gas,  of 
its  aqueous  solution,  or  of  a  carbonate,  to  the  soil,  had  no 
effect  to  increase  the  crop.  {Chem.  Ac7cersman?i,  1868, 
p.  18.) 

Liebig^  considers  carbonic  acid  to  be,  under  all  circum- 
stances,  the  exclusive  source  of  the  carbon  of  agricultural 
vegetation.  To  this  point  we  shall  recur  in  our  study  of 
the  soil. 

Cartoon  fixed  toy  Chloropliyll. — The  fixation  of  carbon 
from  the  carbonic  acid  of  the  air  is  accomplished  in,  or  has 
an  intimate  relation  with,  the  chlorophyll  grains  of  the 
leaf  or  green  stem.  This  is  not  only  evident  from  the 
microscopic  study  of  the  development  of  the  carbohy- 
drates, especially  starch,  w^hose  organization  proceeds  from 
the  chlorophyll,  but  is  an  inference  from  the  experiments 
of  Gris  on  the  effects  of  withholding  iron  from  plants.  In 
absence  of  iron,  the  leaf  may  unfold  and  attain  a  certain 
development ;  but  chlorophyll  is  not  formed,  and  the  plant 
soon  dies,  without  any  real  growth  by  assimilation  of  food 
from  without.  (H.  C.  G.,  p.  200.)  Finally,  experiment 
shows  that  oxygen  is  given  off  (and  carbonic  acid  decom- 
posed with  fixation  of  carbon)  only  from  those  parts  of 


ATMOSPHEKIC    AIR    AS    THE    FOOD    OF    PLAISTTS.  49 

plants  in  which  the  microscope  reveals  chlorophyll,  although 
the  prevailing  color  may  be  other  than  green. 

Influence  of  Light  on  Fixation  of  Carfeon. — As  men- 
tioned, Ingenhouss  (in  1T79)  discovered  that  oxygen  gas 
is  given  off  from  foliage,  and  carbon  fixed  in  the  plant 
only  under  the  influence  of  light.  Experiments  show  that 
when  a  seed  germinates  in  exclusion  of  light  it  not  only 
does  not  gain,  but  steadily  loses  weight  from  the  consump- 
tion of  carbon  (and  hydrogen)  in  slow  oxidation  (respira- 
tion). 

Thus  Boussingaulf  [Compfes  Bendus,  1864,  p.  883) 
caused  two  beans  to  germinate  and  vegetate,  one  in  the 
ordinary  light  and  one  in  darkness,  during  26  days.  The 
gain  in  light  and  loss  in  darkness  in  entire  (dry)  weight, 
and  of  carbon,  etc.,  are  seen  from  the  statement  below. 
In  Light.  In  Darkness. 

Weight  of  seed 0.922  gram 0.926  gram. 

Weight  of  plant 1.293     "     0.566      " 

Gain  =  0.371  gram.             Loss 0.360  gram. 

Carbon,    Gain  =  0.1926     "  Loss... 0.1598      " 

Hydrogen,  "  =  0.0200      "  "    ...0.0232      " 

Oxygen,       "  =  0.1591      "  "    ...0.1766      " 

§  6. 

THE  AMMONLl  OF  THE  ATMOSPHERE  AND  ITS  RELATIONS 
TO  VEGETABLE  NUTRITION. 

Ammonia  is  a  gas,  colorless  and  invisible,  but  having  a 
peculiar  pungency  of  odor  and  an  acrid  taste. 

l®i*eparatioM.— It  may  he  obtained  in  a  state  of  purity  by  heat- 
ing a  mixture  of  chloride  of  ammonium  (sal  ammoniac)  and  quicklime. 
Equal  quantities  of  the  two  substances  just  named  (50  grams  of  each) 
are  separately  pulverized,  introduced  into  a  flask,  and  well  mixed  by 
shaking.  A  straight  tube  8  inches  long  is  now  secured  in  the  neck  of 
the  flask  by  means  of  a  perforated  cork,  and  heat  applied.  The  ammonia 
gas  which  soon  escapes  in  abundance  is  collected  in  dry  bottles,  which 
are  inverted  over  the  tube.  The  gas,  rapidly  entering  the  bottle,  in  a 
few  moments  displaces  the  twice  heavier  atmospheric  air.    As  soon  as  a 


50  HOW    CROPS   FEED. 

feather  wet  "with  vinegar  or  dilute  elilorliydric  acid  becomes  surrounded 
■\vitli  a  dense  smolvc  when  approaclied  to  the  mouth  of  the  bottle,  the 
latter  may  be  removed,  corked,  and  another  put  in  its  place.  Three  or 
four  pint  bottles  of  gas  thus  collected  will  serve  to  illustrate  its  proper- 
ties, as  shortly  to  be  noticed. 

Solilbllity  la  Water, — This  cliaracter  of  ammonia  is  ex- 
hibited by  removing,  under  cold  water,  the  stopper  of  a 
bottle  filled  with  the  gas.  The  water  rushes  with  great 
violence  into  the  bottle  as  into  a  vacuum,  and  entirely  fills 
it,  provided  all  atmospheric  air  had  been  displaced. 

The  aqua  ammonia^  or  spirits  of  hartshorn  of  the  drug- 
gist, is  a  strong  solution  of  ammonia,  prepared  by  passing 
a  stream  of  ammonia  gas  into  cold  water.  At  the  freez- 
ing point,  water  absorbs  1,150  times  its  bulk  of  ammonia. 
"When  such  a  solution  is  warmed,  the  gas  escapes  abund- 
antly, so  that,  at  ordinary  summer  temperatures,  only  one- 
half  the  ammonia  is  retained.  If  the  solution  be  heated 
to  boiling,  all  the  ammonia  is  expelled  before  the  water  has 
nearly  boiled  away.  The  gas  escapes  even  from  very  di- 
lute solutions  when  they  are  exposed  to  the  air,  as  is  at 
once  recognized  by  the  sense  of  smell. 

Compositioili — When  ammonia  gas  is  heated  to  redness 
by  being  made  to  pass  through  an  ignited  tube,  it  is  de- 
composed, loses  its  characteristic  odor  and  other  proper- 
ties, and  is  resolved  into  a  mixture  of  nitrogen  and  hydro- 
gen gases.  These  elements  exist  in  ammonia  in  the  pro- 
portion of  one  part  by  bulk  of  nitrogen,  to  three  parts  of 
hydrogen,  or  by  weight  fourteen  parts  or  one  atom  of 
nitrogen  and  three  parts,  or  three  atoms  of  hydrogen. 
The  subjoined  scheme  exhibits  the  composition  of  ammo° 
nia,  as  expressed  in  symbols,  atoms,  and  percentages. 

Symbol.  At.  vPt.  Per  cent. 

'    N  =        14        ..  82.39 

H3        =  3        ..  17.61 

NH3        =        17        ..        100.00 
Formation  of  Ammonia. — 1.  When  hydrogen  and  ni- 
trogen gases  are  mingled  together  in  the  proportions  to 


ATMOSPHERIC    AIR    AS   THE   FOOD    OE    PLANTS.  51 

form  ammonia,  they  do  not  combine  either  spontaneously  or 
by  aid  of  any  means  yet  devised,  but  remain  for  an  indef- 
inite period  as  a  mere  mixture.  The  oft  repeated  assertion 
that  nascent  hydrogen,  i.  e.,  hydrogen  at  the  moment  of 
liberation  from  some  combination,  may  unite  with  free 
nitrogen  to  form  ammonia,  has  been  cohipletely  refuted  by 
the  experiments  of  Will,  {Ann.  Ch.  u.  Ph.,  XLY,  110.) 
The  ammonia  observed  by  older  experimenters  existed, 
ready  formed,  in  the  materials  they  operated  with. 

2.  It  appears  from  recent  researches  (of  Boettger, 
Schonbeiu,  and  Zabelin)  that  ammonia  is  formed  in  minute 
quantity  from  atmospheric  nitrogen  in  many  cases  of  com- 
bustion, and  is  also  generated  when  vapor  of  water  and 
the  air  act  upon  each  other  in  contact  with  certain  organic 
matters,  at  a  temperature  of  120°  to  160°  F.  To  this  sub- 
ject we  shall  again  recur,    p.  77. 

3.  Ammonia  may  result  from  the  reduction  of  nitrous 
and  nitric  acids,  and  from  the  action  of  alkalies  and  lime 
upon  the  albuminoids,  gelatine,  and  other  similar  organic 
matters.  To  these  modes  of  its  formation  we  shall  recur 
on  subsequent  pages. 

4.  Ammonia  is  most  readily  and  abundantly  formed  from 
organic  nitrogenous  bodies;  e.  g.,  the  albuminoids  and 
similar  substances,  by  decay  or  by  dry  distillation.  It  is 
supposed  to  have  been  called  ammonia  because  one  of  its 
most  common  compounds  (sal  ammoniac)  was  first  prepared 
by  burning  camels'  dung  near  the  temple  of  Jupiter  Ammon 
in  Libya,  Asia  Minor.  The  name  hartshorn,  or  spirits  of 
hartshorn,  by  which  it  is  more  commonly  known,  was 
adopted  from  the  circumstance  of  its  preparation  by  dis- 
tilling the  horns  of  the  stag  or  hart. 

The  ammonia  and  ammoniacal  salts  of  commerce  (car- 
bonate of  ammonia,  sal  ammoniac,  and  sulphate  of  ammo- 
nia) are  exclusively  obtained  from  these  sources. 

When  urine  is  allowed  to  become  stale,  it  shortly  smells 


52  HOW    CEOPS    FEED. 

of  ammonia,  which  copiously  escapes  in  the  form  of  car- 
bonate, and  may  be  separated  by  distillation. 

When  bones  are  heated  in  close  vessels,  as  in  the  manu- 
facture of  bone-black  or  bone-char  for  sugar  refining,  the 
liquid  product  of  the  distillation  is  strongly  charged  with 
carbonate  of  ammonia. 

Commercial  ammonia  is  mostly  derived,  at  present,  from 
the  distillation  of  bituminous  coal,  and  is  a  bye-product  of 
the  manufacture  of  illuminating  gas.  The  gases  and  va- 
pors that  issue  from  the  gas-retort  in  which  the  coal  is  heat- 
ed to  redness,  are  washed  by  passing  through  water.  This 
wash  water  is  always  found  to  contain  a  small  quantity  of 
ammonia,  which  may  be  cheaply  utilized 

The  exhalations  of  volcanoes  and  fumeroles  likewise 
contain  ammonia,  which  is  probably  formed  in  a  similar 
manner. 

In  the  processes  of  combustion  and  decay  the  elements 
of  the  organic  matters  are  thrown  into  new  groupings, 
which  are  mostly  simpler  in  composition  than  the  original 
substances.  A  portion  of  nitrogen  and  a  corresponding 
portion  of  hydrogen  then  associate  themselves  to  form  am- 
monia. 

Ammonia  is  a  Strong  Alkaline  Base.— Those  bases 
which  have  in  general  the  strongest  affinity  for  acids,  are 
potash,  soda,  and  ammonia.  These  bodies  are  very  similar 
in  many  of  their  most  obvious  characters,  and  are  collec- 
tively denominated  the  alkalies.  They  are  alike  freely 
soluble  in  water,  have  a  bitter,  burning  taste,  alike  corrode 
the  skin  and  blister  the  tongue ;  and,  united  with  acids, 
form  the  most  permanent  saline  compounds,  or  salts. 

Carl)Onate  of  Ammonia. — If  a  bottle  be  filled  with  car- 
bonic acid,  (by  holding  it  inverted  over  a  candle  until  the 
latter  becomes  extinguished. when  passed  a  little  way  into 
the  bottle,)  and  its  mouth  be  applied  to  that  of  a  vessel 
containing  ammonia  gas,  the  two  invisible  airs  at  once 


ATMOSPHEEIC    AIR    AS    THE   FOOD    OF   PLAINTS.  53 

combine  to  a  solid  salt,  the  carbonate  of  ammonia,  which 
appears  as  a  white  cloud  where  its  ingredients  come  in 
contact. 

Carbonate  of  ammonia  occurs  in  commerce  under  the 
name  "salts  of  hartshorn,"  and  with  the  addition  of  some 
perfume  forms  the  contents  of  the  so-called  smelling-bot- 
tles. It  rapidly  vaporizes,  exhahng  the  odor  of  ammonia 
very  strongly,  and  is  hence  sometimes  termed  sal  volatile. 
Like  camphor,  this  salt  passes  from  the  solid  state  into 
that  of  invisible  vapor,  at  ordinary  temperatures,  without 
assuming  intermediately  the  liquid  form. 

In  the  atmosphere  the  quantity  of  carbonic  acid  greatly 
preponderates  over  that  of  the  ammonia ;  hence  it  is  im- 
possible that  the  latter  should  exist  in  the  free  state,  and 
we  must  assume  that  it  occurs  there  chiefly  in  combination 
with  carbonic  acid.  The  carbonate  of  ammonia,  whether 
solid  or  gaseous,  is  readily  soluble  in  water,  and  like  free 
ammonia  it  evaporates  from  its  solution  with  the  first 
l^ortions  of  aqueous  vapor,  leaving  the  residual  water  rel- 
atively free  from  it. 

In  the  guano-beds  of  Peru  and  Bolivia,  carbonate  of 
ammonia  is  sometimes  found  in  the  form  of  large  trans- 
parent crystals,  which,  like  the  artificially-prepared  salt, 
rapidly  exhale  away  in  vapor,  if  exposed  to  the  air. 

This  salt,  commonly  called  bicarbonate  of  ammonia,  con- 
tains in  addition  to  carbonic  acid  and  ammonia,  a  portion 
of  water,  which  is  indispensable  to  its  existence.  Its  com- 
position is  as  follows : 

Synibol.  At.  wH.  Per  cent 
NHg                      17  21.5 

H2O  18  22.8 

COo  44  55.7 


NH3.  H2O.  CO2.    79  100.0 

Tests  for  AmBsiomia.— a.  If  salts  of  ammonia  are  rubbed  to- 
gether with  slaked  lime^  best  with  the  addition  of  a  few  drops  of  water, 
the  ammonia  is  liberated  in  the  gaseous  state,  and  betrays  itself  (1)  by 
its  characteristic  odor  ;  (2)  by  its  reaction  on  moistened  test-papers ;  and 


54  HOW    CROPS    FEED. 

(3)  by  giving  rise  to  the  formation  of  wJiite  fames,  when  any  object  (e.  g.y 
a  glass  rod)  moistened  with  hydrocliloric  acid,  is  bronglit  in  contact  with 
it.  These  fumes  arise  from  the  formation  of  solid  ammoniacal  salts  pro- 
duced by  the  contact  of  the  gases. 

h.  Mssler's  Test— For  the  detection  of  exceedingly  minute  traces  of 
ammonia,  a  reaction  first  pointed  out  by  Nessler  may  be  employed.  Di- 
gest at  a  gentle  heat  2  grammes  of  iodide  of  potassium,  and  3  grammes 
of  iodide  of  mercury,  in  5  cub.  cent,  of  water;  add  20  cub.  cent,  of  wa- 
ter, let  the  mixture  stand  for  some  time,  then  filter;  add  to  the  filtrate 
SO  cub.  cent,  of  pure  concentrated  solution  of  potassa  (1  :  4);  and,  should  j^ 
a  precipitate  form,  filter  again.  If  to  this  solution  is  added,  in  small ' 
quantity,  a  liquid  containing  ammonia  or  an  ammonia-salt,  a  reddish  hrowii 
precipitate,  or  with  exceedingly  small  quantities  of  ammonia,  a  yellow 
coloratioji  is  produced  from  the  formation  of  dimercurammonic  iodide, 
NHgo  I.OH2. 

c.  Bo7ilig''s  Test. — According  to  Bohlig,  chloride  of  mercury  (corrosive 
sublimate)  is  the  most  sensitive  reagent  for  ammonia,  when  in  the  free 
state  or  as  carbonate.  It  gives  a  white  precipitate,  or  in  very  dilute  so- 
lutions (even  when  containing  but  ^1 200,000  of  ammonia)  a  white  turbidity, 
due  to  the  separation  of  mercurammonic  chloride,  NH2  Hg.Cl.  In  solu- 
tions of-the  salts  of  ammonia  with  other  acids  than  carbonic,  a  clear 
solution  of  mixed  carbonate  of  potassa  and  chloride  of  mercury  must  be 
employed,  which  is  prepared  by  adding  10  drops  of  a  solution  of  the 
purest  carbonate  of  potassa,  (1  of  salt  to  50  of  Avater,)  and  5  drops  of  a 
solution  of  chloride  of  mercury  to  80  c.  c.  of  water  exempt  from  am- 
monia (such  is  the  water  of  many  springs,  but  ordinary  distilled  water 
rarely).  This  reagent  may  be  kept  in  closed  vessels  for  a  time  without 
change.  If  much  more  concentrated,  oxide  of  mercury  separates  from  it. 
By  its  use  the  ammonia  salt  is  first  converted  into  carbonate  by  double 
decomposition  with  the  carbonate  of  potassa,  and  the  further  reaction 
proceeds  as  before  mentioned. 

Occiirreace  of  imiaoiiia  m  tlie  ilMOspliere, — The  ex- 
istence of  ammonia  in  the  atmosphere  was  first  noticed  by 
De  SaussLire,  and  has  been  proved  repeatedly  by  direct 
experiment.  That  the  quantity  is  exceedingly  minute  has 
been  equally  well  established.  * 

Owing  partly  to  the  variable  extent  to  which  ammonia 
occurs  in  the  atmosphere,  but  chiefly  to  the  difficulty  of 
collecting  and  estimating  such  small  amounts,  the  state- 
ments of  those  who  have  experimented  upon  this  subject 
are  devoid  of  agreement. 

We  present  here  a  tabulated  view  of  the  most  trust- 
worthy results  hitherto  published : 


ATirOSPHERIC    AIK    AS    THE    FOOD    OF    PLANTS.  55 

1,000,000,000  parts  of  atmospheric  air  contain  of  ammonia,  according  to 

Graeger,    at  Miitilliausen,  German}^,  average,    333  parts. 

Fresenius,  "  Wiesbaden,  .  "  "  133      " 

Pierre,        "  Caen,  France,  1851-52,        "        3500      " 

"  "      "  "        1853-53,         "  500      " 

Bineau,       "  Lyons,      "        1852-53,         "  250      " 

'•  "  Caluire,     "  "       winter,         40      " 

"  "        "         "  "       Slimmer,      80      " 

Ville,  "  Paris,        "        1819-50,  average,      21      " 

''  Grenelle,  "        1851,  "  21       " 

Graham  has  shown  by  experiment  (Yille,  Mecherches 
sur  la  ITegetation^  Paris,  1853,  p.  5,)  that  a  quantity  of 
ammonia  like  that  found  by  Fresenius  is  sufficient  to  be 
readily  detected  by  its  effect  on  a  red  litmus  paper,  whicb 
is  not  altered  in  the  air.  This  demonstrates  that  the  at- 
mosphere where  Graham  experimented  (London)  contained 
less  than  ^^^l^g^ggg^g^j^ths  of  ammonia  in  the  state  of  bicar- 
bonate. The  experiments  of  Fresenius  and  of  Grager 
were  made  with  comparatively  small  volumes  of  air,  and 
those  of  the  latter,  as  well  as  those  of  Pierre,  and  some  of 
Bineau's,  were  made  in  the  vicinity  of  dwellings,  or  even 
in  cities,  Avhere  the  results  might  easily  be  influenced  by 
local  emanations.  Bineau's  results  were  obtained  by  a 
method  scarcely  admitting  of  much  accuracy. 

The  investigations  of  Yille  {Hecherches^  Paris,  1853,) 
are,  perhaps,  the  most  trustworthy,  having  been  made  on 
a  large  scale,  and  apparently  with  every  precaution.  Yf  e 
may  accordingly  assume  that  the  average  quantity  of  am- 
monia in  the  air  is  one  part  in  fifty  millions,  although  the 
amount  is  subject  to  considerable  fluctuation. 

From  the  circumstance  that  ammonia  and  its  carbonate 
are  so  readily  soluble  in  water,  we  should  expect  that  in 
rainy  weather  the  atmosphere  would  be  washed  of  its  am- 
monia ;  while  after  prolonged  dry  weather  it  would  con- 
tain more  than  usual,  since  ammonia  escapes  from  its 
solutions  with  the  first  portions  of  aqueous  vapor. 

The  ibsorption  of  iiuMciiiia  I>y  Vegetation.— The  gen- 
eral fact  that  ammonia  in  its  compounds  is  appropriated 


56 


HOW    CROPS    FEED 


by  plants  as  food  is  most  abundantly  established.  The 
salts  of  ammonia  applied  as  manures  in  actual  farm  prac- 
tice have  produced  the  most  striking  effects  in  thousands 
of  instances. 

By  watering  potted  plants  with  A^ery  dilute  solutions  of 
ammonia,  their  luxuriance  is  made  to  surpass  by  far  that 
of  similar  plants,  which  grow  in  precisely  the  same  condi- 
tions, save  that  they  are  supplied  with  simple  water. 

Ville  has  stated,  1851-2,  that  vegetation  in  conserva- 
tories may  be  remarkably  i)romoted  by  impregnating  the 
air  with  gaseous  carbonate  of  ammonia.  For  this  purpose 
lumps  of  the  solid  salt  are  so  disposed  on  the  heating  ap- 
paratus of  the  green-house  as  to  gradually  vaporize,  or 
vessels  containing  a  mixture  of  quicklime  and  sal  ammo- 
niac may  be  employed.  Care  must  be  taken  that  the  air  does 
not  contain  at  any  time  more  than  four  ten-thousandths 
of  its  weight  of  the  salt ;  otherwise  the  foliage  of  tender 
plants  is  injured.  Like  results  were  obtained  by  Petzholdt 
and  Chlebodarow  in  1852-3. 

Absorptl®!!  of  AmiEoiila  by  Foli- 
age.— Although  such  facts  indicate 
that  ammonia  is  directly  absorbed  by 
foliage,  they  fail  to  prove  that  the 
soil  is  not  the  medium  through  which 
the  absorption  really  takes  i^lace.  We 
remember  that  according  to  linger 
and  Duchartre  water  enters  the 
higher  plants  almost  exclusively  by 
the  roots,  after  it  has  been  absorbed 
by  the  soil.  To  Peters  and  Sachs 
( Ghem.  AcJcersmcmn,  6,  158)  we  owe 
an  experiment  which  appears  to  de- 
monstrate that  ammonia,  like  carbonic 
acid,  is  imbibed  by  the  leaves  of 
Fig-  6.  plants.     The  figure  represents  the  ap- 

paratus employed.  It  consisted  of  a  glass  bell,  resting  below, 


ATMOSPHERIC   AIR   AS    THE    FOOD    OF   PLANTS.  57 

air-tiglit,  upon  a  glass  plate,  and  having  two  glass  tubes 
cemented  into  its  neck  above,  as  in  fig^.  6.  Througrh 
an  aperture  in  the  centre  of  the  glass  plate  the  stem  of 
the  plant  experimented  on  was  introduced,  so  that  its  fo- 
liage should  occupy  the  bell,  while  the  roots  Avere  situated 
in  a  pot  of  earth  beneath.  Two  young  bean-plants,  grow- 
ing in  river  sand,  were  arranged,  each  in  a  separate  appa- 
ratus, as  in  the  figure,  on  June  19th,  1859,  their  stems  be- 
ing cemented  tightly  into  the  opening  below,  and  through 
the  tubes  the  foliage  of  each  plant  received  daily  the  same 
quantities  of  moist  atmospheric  air  mixed  with  4-5  per 
cent  of  carbonic  acid.  One  plant  w^as  supplied  in  addition 
with  a  quantity  of  carbonate  of  ammonia,  which  was  in- 
troduced by  causing  the  air  that  was  forced  into  the  bell 
to  stream  through  a  dilute  solution  of  this  salt.  Both 
plants  grew  well,  until  the  experiment  was  terminated,  on 
the  11th  of  August,  when  it  was  found  that  the  plant 
whose  foliage  was  not  supplied  with  carbonate  of  ammo- 
nia w^eighed,  dry,  4.14  gm.,  while  the  other,  which  was 
supplied  with  the  vapor  of  this  salt,  weighed,  dry,  6.74 
gms.  The  first  plant  had  20  full-sized  leaves  and  2  side 
shoots ;  the  second  had  40  leaves  and  7  shoots,  besides  a 
much  larger  mass  of  roots.  The  first  contained  0.106 
gm.  of  nitrogen ;  the  second,  double  that  amount,  0.208 
gm.  Other  trials  on  various  plants  failed  from  the  diffi- 
culty of  making  them  grow  in  the  needful  circumstances. 

The  absorption  of  ammonia  by  foliage  does  not  appear, 
like  that  of  carbonic  acid,  to  depend  upon  the  action  of 
sunlight;  but,  as  Mulder  has  remarked,*  may  go  on  at 
all  times,  especially  since  the  juices  of  plants  are  very  fre- 
quently more  or  less  charged  with  acids  which  directly 
unite  chemically  with  ammonia. 

When  absorbed,  ammonia  is  chiefly  applied  by  agricul- 


♦  Chemie  der  Ackerkrume,  Yol.  2,  p.  211. 

3* 


58  HOW    CROPS    FEED. 

tural  plants  to  the  j)roduction  of  the  albuminoids.*  We 
measure  the  nutritive  effect  of  ammonia  salts  applied  as 
fertilizers  by  the  amount  of  nitrogen  which  vegetation  as- 
similates from  them. 

Effects  of  IffiMOMla  OB  Tegetatioa,  —  The  remarkable 
effect  of  carbonate  of  ammonia  upon  vegetation  is  well 
described  by  Yille.  We  know  that  most  plants  at  a  cer- 
tain period  of  growth  under  ordinary  circumstances  cease 
to  produce  new  branches  and  foliage,  or  to  expand  those 
already  formed,  and  begin  a  new  phase  of  development  in 
providing  for  the  perpetuation  of  the  species  by  producing 
flowers  and  fruit.  If,  however,  such  plants  are  exposed 
to  as  much  carbonate  of  ammonia  gas  as  they  are  capable 
of  enduring,  at  the  time  when  flowers  are  beginning  to 
form,  these  are  often  totally  checked,  and  the  activity  of 
growth  is  transferred  to  stems  and  leaves,  which  assume 
a  new  vigor  and  multiply  with  extraordinary  luxuriance. 
If  flowers  are  formed,  they  are  sterile,  and  yield  no  seed. 

Another  noticeable  effect  of  ammonia — one,  however, 
which  it  shares  with  other  substances — is  its  power  of  deep- 
ening the  color  of  the  foliage  of  plants.  This  is  an  indi- 
cation of  increased  vegetative  activity  and  health,  as  a 
pale  or  yellow  tint  belongs  to  a  sickly  or  ill-fed  growth. 

A  third  result  is  that  not  only  the  mass  of  vegetation 
is  increased,  but  the  relative  proportion  of  nitrogen  in  it  is 
heightened.  This  result  was  obtained  in  the  experiment  of 
Peters  and  Sachs  just  described.  To  adduce  a  single  other 
instance,  Yille  found  that  grains  of  wheat,  grown  in  pure 
air,  contained  2.09  per  cent  of  nitrogen,  while  those  which 
were  produced  under  the  influence  of  ammonia  contained 
3.40  per  cent. 


*  In  tobacco,  to  tla3  production  of  nicotine  ;  in  coffee,  of  caffeine  ;  and  in  many- 
other  plants  to  analogous  substances.  Plants  appear  oftentimes  to  contain 
small  quantities  of  ammonia  salts  and  nitrates,  as  well  as  of  asparagin,  (C4  H3 
No  03,)a  substance  first  found  in  asparagus,  and  which  is  formed  in  many 
plants  when  they  vegetate  in  exclusion  of  light. 


ATMOSPHERIC    AIR    AS   THE    FOOD    OF    FLANTSo  59 

Do  Heaitliy  Plants  Exhale  AmMoma !— The  idea  having 
been  advanced  that  in  the  act  of  vegetation  a  loss  of  ni- 
trogen may  occur,  possibly  in  the  form  of  ammonia,  Knop 
made  an  experiment  with  a  water-plant,  the  Typha  lati- 
folia^  a  species  of  Cat-tail,  to  determine  this  point.  The 
plant,  growing  undisturbed  in  a  pond,  was  enclosed  in  a 
glass  tube  one  and  a  half  inches  in  diameter,  and  six  feet 
long.  The  tube  was  tied  to  a  stake  driven  for  the  purpose ; 
its  lower  end  reached  a  short  distance  below  the  surface 
of  the  water,  while  the  upper  end  was  covered  air-tight 
with  a  cap  of  India  rubber.  This  cap  was  penetrated  by 
a  narrow  glass  tube,  which  communicated  with  a  vessel 
filled  with  splinters  of  glass,  moistened  with  pure  hydro- 
chloric acid.  As  the  large  tube  was  placed  over  the  plant, 
a  narrow  U-shaped  tube  was  immersed  in  the  water  to 
half  its  length,  so  that  one  of  its  arms  came  within, 
and  the  other  without,  the  former.  To  the  outer  extremity 
of  the  TJ-tube  was  attached  an  apparatus,  for  the  perfect 
absorption  of  ammonia.  By  aspirating  at  the  upper  end 
of  the  long  tube,  a  current  of  ammonia-free  air  was  thus 
made  to  enter  the  bottom  of  the  apparatus,  stream  upward 
along  the  plant,  and  pass  through  the  tube  of  glass-splint- 
ers wet  with  hydrochloric  acid.  Were  any  ammonia 
evolved  within  the  long  tube,  it  would  be  collected  by  the 
acid  last  named.  To  guard  against  any  ammonia  that 
possibly  might  arise  from  decaying  matters  in  the  water, 
a  thin  stratum  of  oil  was  made  to  float  on  the  water  with- 
in the  tube.  Through  this  arrangement  a  slow  stream  of 
air  was  passed  for  fifty  hours.  At  the  expiration  of  that 
time  the  hydrochloric  acid  was  examined  for  ammonia; 
but  none  was  discovered.  Our  tests  for  ammonia  are  so 
delicate,  that  we  may  well  assume  that  this  gas  is  not  ex- 
haled by  the  Typha  latifolia. 

The  statements  to  be  found  in  early  authors  (Sprengel, 
Schiibler,  Johnston),  to  the  effect  that  ammonia  is  exhaled 
by  some  plants,  deserve  further  examination. 


60  HOW    CROPS    FEED. 

The  CJienopodlura  vulvaria  exhales  from  its  foliage  a 
body  chemically  related  to  ammonia,  and  that  has  been 
mistaken  for  it.  This  substance,  known  to  the  chemist  as 
trimethylamine,  is  also  contained  in  the  flowers  of  Cra- 
tcegus  oxycantha,  and  is  the  cause  of  the  detestable  odor 
of  these  plants,  which  is  that  of  putrid  salt  fish.*  (Wicke, 
LieUg's  Ann.,  124,  p.  338.) 

Certain  fungi  (toad-stools)  emit  trimethylamine,  or  some 
analogous  compound.  (Lehmann,  Sachs'  Experimental 
Physialogie  der  Pflanzen,  p.  273,  note.) 

It  is  not  impossible  that  ammonia,  also,  may  be  exhaled 
from  these  plants,  but  we  have  as  yet  no  proof  that  such 
is  the  case. 

Ammonia  of  the  Atmospheric  Waters. — The  ammonia 
proper  to  the  atmosphere  has  little  effect  upon  plants 
through  their  foliage  when  they  are  sheltered  from  dew 
and  rain.  Such,  at  least,  is  the  result  of  certain  experi- 
ments. 

Boussingault  (Agronomie,  Chunie  Agricole,  et  Physi- 
ologie,  T.  I,  p.  141)  made  ten  distinct  trials  on  luj)ins, 
beans,  oats,  wheat,  and  cress.  The  seeds  were  sown  in  a 
soil,  and  the  plants  were  watered  with  water  both  exempt 
from  nitrogen.  The  plants  were  shielded  by  glazed  cases 
from  rain  and  dew,  but  had  full  access  of  air.  The  result 
of  the  ten  experiments  taken  together  was  as  follows : 

Weight  of  seeds 4.965  grm's. 

"   dry  harvest 18.730      " 

Nitrogen  in  harvest  and  soil. .  .2499      " 
"         "  seeds 2307      " 

Gain  of  nitrogen 0192  grm's    =    7.6  per  cent  of   the 

total  quantity. 

When  rahis  fall,  or  dews  deposit  upon  the  surface  of  the 

*  Trimethylamine  CsHqN  =  N  (CH3)3  may  be  viewed  as  ammonia  NH3,  in 
which  the  three  atoms  of  hydrogen  are  replaced  by  three  atoms  of  methyl 
CH3.  It  is  a  gas  like  ammonia,  and  has  its  pungency,  hnt  accompanied  with  the 
odor  of  stale  fish.  It  is  prepared  from  herring  pickle,  and  used  in  medicine  un- 
der the  name  propylamine. 


ATMOSPHEETG    AIR    AS    THE    FOOD    OF    PLANTS.  61 

soil,  or  upon  the  foliage  of  a  cultivated  field,  they  bring 
down  to  the  reach  of  vegetation  in  a  given  time  a  quantity 
of  ammonia,  far  greater  than  what  is  diifased  throughout 
the  limited  volume  of  air  which  contributes  to  the  nour- 
ishment of  plants.  The  solubility  of  carbonate  of  ammo- 
nia in  water  has  already  been  mentioned.  In  a  rain-fall 
we  have  the  atmosphere  actually  washed  to  a  great  de- 
gree of  its  ammonia,  so  that  nearly  the  entire  quantity  of 
this  substance  which  exists  between  the  clouds  and  the 
earth,  or  in  that  mass  of  atmosphere  through  which  the 
rain  passes,  is  gathered  by  the  latter  and  accumulated 
within  a  small  space. 

Proportion  of  Ammoaia  in  Rain-water,  etc, — The  pro- 
portion of  ammonia  *  which  the  atmospheric  waters  thus 
collect  and  bring  down  upon  the  surface  of  the  soil,  or 
upon  the  foliage  of  plants,  has  been  the  subject  of  inves- 
tigations by  Boussingault,  Bineau,  Way,  Knop,  Bobiere, 
and  Bretschneider.  The  general  result  of  their  accordant 
investigations  is  as  follows :  In  rain-water  the  quantity  of 
ammonia  in  the  entire  fall  is  very  variable,  ranging  in  the 
country  from  1  to  33  parts  in  10  million.  In  cities  the 
amount  is  larger,  tenfold  the  above  quantities  having  been 
observed. 

The  first  portions  of  rain  that  fall  usually  contain  much 
more  ammonia  than  the  latter  portions,  for  the  reason  that 
a  certain  amount  of  water  sufiices  to  wash  the  air,  and 
what  rain  subsequently  falls  only  dilutes  the  solution  at 
first  formed.  In  a  long-continued  rain,  the  water  that 
finally  falls  is  almost  devoid  of  ammonia.  In  rains  of 
short  duration,  as  well  as  in  dews  and  fogs,  which  occasion- 
ally are  so  heavy  as  to  admit  of  collecting  to  a  sufiicient 
extent  for  analysis,  the  proportion  of  ammonia  is  greatest, 
and  is  the  greater  the  longer  the  time  that  has  elapsed 
since  a  previous  precipitation  of  water. 

*  In  all  quantitative  statements  regarding  ammonia,  NH3  is  to  be  understood, 
andnotNHiO. 


62 


HOW    CEOPS    FEED. 


Boussingault  found  in  the  first  tenth  of  a  slow-falling 
rain  (24th  Sept.,  1853)  66  parts  of  ammonia,  in  the  last 
three-tenths  but  13  parts,  to  10  million  of  water.  In  dew 
he  found  40  to  62 ;  in  fog,  25  to  72 ;  and  in  one  extraordi- 
nary instance  497  parts  in  ten  million. 

Boussingault  found  that  the  average  pro^Dortion  of  am- 
monia in  the  atmosplieric  waters  (dew  and  fogs  included) 
which  he  was  able  to  collect  at  Liebfrauenberg  (near  Stras- 
burg,  France)  from  the  26th  of  May  to  the  8th  of  ^N'ov. 
1853,  was  6  parts  in  10  million  {Agronomie^  etc.,  T.  II, 
238).  Knop  found  in  the  rains,  snow,  and  hail,  that  fell  at 
Moeckern,  near  Leipzig,  from  April  18th  to  Jan.  15th, 
1860,  an  average  of  14  parts  in  10  million.  ( Yersuchs- 
iStationen,  Vol.  3,  p.  120.) 

Pincus  and  RoUig  obtained  from  the  atmospheric  wa- 
ters collected  at  Insterburg,  North  Prussia,  during  the  12 
months  ending  with  March,  1865,  in  26  analyses,  an  average 
of  7  parts  of  ammonia  in  10  million  of  water.  The  average 
for  the  next  following  12  months  was  9  parts  in  10  million. 

Bretschneider  found  in  the  atmospheric  waters  collected 
by  him  at  Ida-Marienhiitte,  in  Silesia,  from  April,  1865,  to 
April,  1866,  as  the  average  of  9  estimations,  30  parts  of 
ammonia  in  10  million  of  water.  In  the  next  year  the 
quantity  was  23  parts  in  10  million. 

In  10  million  parts  of  rain-water,  etc.,  collected  at  the 
following  places  in  Prussia,  were  contained  of  ammonia — 
at  Regenwalde,  in  1865,  24;  in  1867,  28;  at  Dahme,  in 
1865,17;  at  Kuschen,  in  1865,5^-;  and  in  1866,  7|- parts. 
{Preus.  Ann.  d.  Landwirthschaft^  1867.)  The  monthly 
averages  fluctuated  without  regularity,  but  mostly  within 
narrow  limits.  Occasionally  they  fell  to  2  or  3  parts,  once 
to  nothing,  and  rose  to  35  or  40,  and  once  to  144  parts  in 
10  million. 

Quantity  of  Ammonia  per  Acre  Brought  ©own  by  Main, 
etc. — In  1855  and  '56,  Messrs.  Lawes  &  Gilbert,  at  Roth- 
amstead,  England,  collected  on  a  large  rain-gauge  having 


ATMOSPHERIC    AIR    AS   THE    FOOD    OF    PLANTS.  63 

a  surface  of  -]o\o  of  an  acre,  the  entire  rain-fall  (dews,  etc., 
included)  for  those  years.  Prof.  Way,  at  that  time  chem- 
ist to  the  Royal  Ag.  Soc.  of  England,  analyzed  the  waters, 
and  found  that  the  total  amount  of  ammonia  contained  in 
them  was  equal  to  7  lbs.  in  1855,  and  9|-  lbs.  in  1856,  for 
an  acre  of  surface.  These  amounts  were  yielded  by 
663,000  and  616,000  gallons  of  rain-water  respectively. 

In  the  Avaters  gathered  at  Insterburg  during  the  twelve- 
month ending  March,  1865,  Pincus  and  Rollig  obtained 
6.38  lbs.  of  ammonia  per  acre. 

Bretschneider  found  in  the  waters  collected  at  Ida-Ma- 
rienhutte  from  April,  1865,  to  April,  1866,  12  lbs.  of  am- 
monia per  acre  of  surface. 

The  significance  of  these  quantities  may  be  most  appro- 
priately discussed  after  we  have  noticed  the  nitric  acid  of 
the  atmosphere,  a  substance  whose  functions  towards  vege- 
tation are  closely  related  to  those  of  ammonia. 


OZONE. 

When  lightning  strikes  the  earth  or  an  object  near 
its  surface,  a  person  in  the  vicinity  at  once  perceives  a 
peculiar,  so-called  "  sulphureous  "  odor,  whicli  must  belong 
to  something  developed  in  the  atmosphere  by  electricity. 
The  same  smell  may  be  noticed  in  a  room  in  which  an 
electrical  machine  has  been  for  some  time  in  vigorous 
action. 

The  substance  which  is  thus  produced  is  termed  o^o?ie, 
from  a  Greek  word  signifying  to  smell.  It  is  a  colorless 
gas,  possessing  most  remarkable  properties,  and  is  of  the 
highest  importance  in  agricultural  science,  although  our 
knowledge  of  it  is  still  exceedingly  imperfect. 

Ozone  is  not  known  in  a  pure  state  free  from  other 
bodies  ;   but  hitherto  has  only  been  obtained  mixed  with 


64  HOW    CROPS    FEED. 

several  times  its  weight  of  air  or  oxygen.*  It  is  entirely- 
insoluble  in  water.  It  has,  when  breathed,  an  irritating: 
action  on  the  lungs,  and  excites  coughing  like  chlorine  gas. 
Small  animals  are  shortly  destroyed  in  an  atmosphere 
charged  with  it.  It  is  itself  instantly  destroyed  by  a  heat 
considerably  below  that  of  redness. 

The  special  character  of  ozone  that  is  of  interest  in 
connection  y/ith  questions  of  agriculture  is  its  oxidizing 
poicer.  Silver  is  a  metal  which  totally  refuses  to  combine 
with  oxygen  under  ordinary  circumstances,  as  shown  by 
its  maintaining  its  brilliancy  without  symptom  of  rust  or 
tarnish  when  exposed  to  pure  air  at  common  or  at  greatly 
elevated  temperatures.  When  a  slip  of  moistened  silver 
is  placed  in  a  vessel  the  air  of  which  is  charged  with 
ozone,  the  metal  after  no  long  time  becomes  coated  with  a 
black  crust,  and  at  the  same  time  the  ozone  disappears. 

By  the  apj^lication  of  a  gentle  heat  to  the  blackened 
silver,  ordinary  oxygen  gas^  having  the  properties  already 
mentioned  as  belonging  to  this  element,  escapes,  and  the 
slip  recovers  its  original  silvery  color.  The  black  crust  is 
in  fact  an  oxide  of  silver  (AgO,)  which  readily  suffers  de- 
composition by  heat.  In  a  similar  manner  iron,  copper, 
lead,  and  other  metals,  are  rapidly  oxidized. 

A  variety  of  vegetable  pigments,  such  as  indigo,  litmus,  etc.,  are 
speedily  Ueached  by  ozone.     This  action,  also,  is  simply  one  of  oxidation. 

Gorup-Besanez  {Ann.  Ch.  ic.  Ph.^  110,  86;  also,  PhysiologiscJie  Cheinie) 
has  examined  the  deportment  of  a  number  of  organic  bodies  towards 
ozone.  He  finds  that  egg-albumin  and  casein  of  milk  are  rapidly  altered 
by  it,  Avhile  flesh  fibrin  is  unaflTected. 

Starch,  the  sugars,  the  organic  acids,  and  fats,  are,  when  pure,  unaf- 
fected by  ozone.  In  presence  of  (dissolved  in)  alkalies,  however,  they 
are  oxidized  with  more  or  less  rapidity.  It  is  remarkable  that  oxidation 
by  ozone  takes  place  only  in  the  ■presence  of  water.  Dry  substances  are 
unaffected  by  it. 

The  peculiar  deportment  towards  ozone  of  certain  volatile  oils  will  be 
presently  noticed. 


*  Babo  and  Claus  (Ann.  Ch.  u.  Ph.,  2d  Sup.,  p.  304)  prepared  a  mixture  of  oxy- 
gen and  ozone  containing  nearly  6  per  cent  of  the  latter. 


ATMOSPHERIC   AIR   AS    THE    FOOD    OF    PLANTS.  65 

Tests  fba*  Ozone. — Certain  phenomena  of  oxidation  that  are 
attended  with  changes  of  color  serve  for  the  recognition  of  ozone. 

"We  have  already  seen  (H.  C.  G.,p,  64)  that  starch,  when  brought  in 
contact  with  iodine,  at  once  assumes  a  deep  blue  or  purple  color.  When 
the  compound  of  iodine  with  potassium,  known  as  iodide  of  potas- 
sium, is  acted  on  by  ozone,  its  potassium  is  at  once  oxidized  (to  pot- 
ash,) and  the  iodine  is  set  free.  If  now  paper  be  impregnated  with  a 
mixture  of  starch-paste  and  solution  of  iodide  of  potassium,*  Ave  have  a 
test  of  the  presence  of  ozone,  at  once  most  characteristic  and  delicate. 

Such  paper,  moistened  and  placed  in  ozonousf  air,  is  speedily  turned 
blue  by  the  action  of  the  liberated  iodine  upon  the  starch.  By  the  use 
of  this  test  the  presence  and  abundance  of  ozone  in  the  atraosijhere  has 
been  measured. 

Ozoae  is  Active  Oxygen. — That  ozone  is  nothing  more 
or  less  than  oxygen  in  a  peculiar,  active  condition,  is  shown 
by  the  following  experiment.  When  perfectly  pure  and 
dry  oxygen  is  enclosed  in  a  glass  tube  containing  moist 
metallic  silver  in  a  state  of  fine  division,  it  is  possible  by 
long-continued  transmission  of  electrical  discharges  to 
cause  the  gaseous  oxygen  entirely  to  disappear.  On  heat- 
ing the  silver,  which  has  become  blackened  (oxidized)  by 
the  process,  the  original  quantity  of  oxygen  is  recovered 
in  its  ordinary  state.  The  oxygen  is  thus  converted  under 
the  influence  of  electricity  into  ozone,  which  unites  with 
the  silver  and  disappears  in  the  solid  combination. 

The  independent  experiments  of  Andrews,  Babo,  and 
Soret,  demonstrate  that  ozone  has  a  greater  density  than 
oxygen,  since  the  latter  diminishes  in  volume  when  elec- 
trized. Ozone  is  therefore  conde7ised  oxygen^  i.  e.,  its 
molecule  contains  more  atoms  than  the  molecule  of  ordi- 
nary oxygen  gas. 


*  Mis  10  parts  of  starch  with  200  parts  of  cold  water  and  1  part  of  recently 
fused  iodide  of  potassium,  by  rubbing  them  together  in  a  mortar ;  then  heat  to 
boiling,  and  strain  through  linen.  Smear  pure  filter  paper  with  this  paste,  and  dry 
The  paper  should  be  perfectly  white,  and  must  be  preserved  in  a  well-stoppered 
bottle. 

t  I.  e.,  charged  with  ozone. 

X  Recent  observations  by  Babo  and  Clans,  and  by  Soret,  show  that  the  density 
of  ozone  is  one  and  a  half  times  greater  than  that  of  oxygen. 


66  HOW  cr.ops  feed. 

Allotropisnia — This  occurrence  of  an  element  in  two  or  even 
more  forms  is  not  without  other  illustrations,  and  is  termed  Allotropisra. 
Phosphorus  occurs  in  two  conditions,  viz.,  red  phosphorus,  which  crys- 
tallizes in  rhombohedrons,  and  like  ordinary  oxygen  is  comparatively 
inactive  in  its  affinities ;  and  colorless  phosphorus,  which  crystallizes  in 
octahedrons,  and,  like  ozone,  has  vigorous  tendencies  to  unite  with  other 
bodies.  Carbon  is  also  found  in  three  allotropic  forms,  viz.,  diamond, 
plumbago,  and  charcoal,  which  differ  exceedingly  in  their  chemical  and 
physical  characters. 

O^one  Formed  fey  Ctiemlcal  ictioaa — Not  only  is  ozone 
produced  by  electrical  disturbance,  but  it  has  likewise 
been  shown  to  originate  from  chemical  action ;  and,  in 
fact,  from  the  very  kind  of  action  which  it  itself  so  vig- 
orously manifests,  viz.,  oxidation. 

When  a  clean  stick  of  colorless  phosphorus  is  placed  at 
the  bottom  of  a  large  glass  vessel,  and  is  half  covered 
Avith  tepid  water,  there  immediately  appear  white  vapors, 
which  shortly  fill  the  apparatus.  In  a  little  time  the  pe- 
culiar odor  of  ozone  is  evident,  and  the  air  of  the  vessel 
gives,  with  iodide-of-potassium-starch-paper,  the  blue  color 
which  indicates  ozone.  In  this  experiment  ordinary  oxy- 
gen, in  the  act  of  uniting  with  phosphorus,  is  partially 
converted  into  its  active  modification ;  and  although  the 
larger  share  of  the  ozone  formed  is  probably  destroyed  by 
uniting  with  phosphorus,  a  portion  escapes  combination 
and  is  recognizable  in  the  surrounding  air. 

The  ozone  thus  developed  is  mingled  with  other  bodies, 
(phosphorous  acid,  etc.,)  which  cause  the  white  cloud. 
The  quantity  of  ozone  that  appears  in  this  experiment, 
though  very  small, — under  the  most  favorable  circum- 
stances but  ^  1^300  of  the  weight  of  the  air, — is  still  sufficient 
to  exhibit  all  the  reactions  that  have  been  described. 

Schonbein  has  shown  that  various  organic  bodies  which 
are  susceptible  of  oxidation,  viz.,  citric  and  tartaric  acids, 
when  dissolved  in  water  and  agitated  with  air  in  the  sun- 
light for  half  an  hour,  acquire  the  reactions  of  ozone. 
Ether  and  alcohol,  kept  in  partially  filled  bottles,  also  be- 
come capable  of  producing  oxidizing  effects.     Many  of  the 


ATMOSPHERIC    AIR    AS    THE    FOOD    OF    TLANTS.  67 

vegetable  oils,  as  oil  of  turpentine,  oil  of  lemon,  oil  of 
cinnamon,  linseed  oil,  etc.,  possess  the  property  of  ozoniz- 
ing oxygen,  or  at  least  acquire  oxidizing  properties  when 
exposed  to  the  air.  Hence  the  bleaching  and  corrosion 
of  the  cork  of  a  partially  filled  turpentine  bottle. 

It  is  a  highly  probable  hypothesis  that  ozone  may  be 
formed  in  many  or  even  all  cases  of  slow  oxidation,  and 
that  although  the  chief  part  of  the  ozone  thus  developed 
must  unite  at  once  with  the  oxidable  substance,  a  portion 
of  it  may  diffuse  into  the  atmosphere  and  escape  immediate 
combination. 

Ozone  is  likewise  produced  in  a  variety  of  chemical  re- 
actions, whereby  oxygen  is  liberated  from  combination  at 
ordinary  temperatures.  ^Yhen  water  is  evolved  by  gal- 
vanic electricity  into  free  oxygen  and  free  hydrogen,  the 
former  is  accompanied  with  a  small  proportion  of  ozone. 
The  same  is  true  in  the  electrolysis  of  carbonic  acid.  So, 
too,^  when  permanganate  of  potash,  binoxide  of  barium, 
or  chromic  acid,  is  mixed  v/ith  strong  sulphuric  acid,  ox- 
ygen gas  is  disengaged  which  contains  an  admixture  of 
ozone.* 

Is  Ozone  Produced  by  Yegetatlos  ? — It  is  an  interesting 
question  whether  the  oxygen  so  freely  exhaled  from  the 
foliage  of  plants  under  the  influence  of  sunlight  is  accom- 
panied by  ozone.     Various  experimenters  have  occupied 


*  It  appears  probable  that  ozone  is  developed  in  all  cases  of  rapid  oxidation  at 
high  temperatures.  This  has  been  long  suspected,  and  Meissner  obtained  strong 
indirect  evidence  of  the  fact.  Since  the  above  was  written,  Pincus  has  announ- 
ced that  ozone  is  produced  when  hydrogen  burns  in  the  air,  or  in  pure  oxygen 
gas.  The  quantity  of  ozone  thus  developed  is  sufiScient  to  be  recognized  by  the 
odor.  To  observe  this  fact,  a  jet  of  hydrogen  should  issue  from  a  fine  orifice  and 
burn  with  a  small  flame,  not  exceeding  9^ -inch  in  length.  A  clean,  dry,  and  cold 
beaker  glass  is  held  over  the  flame  for  a  few  seconds,  when  its  contents  will  smell 
as  decidedly  of  ozone  as  the  interior  of  a  Leyden  jar  that  has  just  been  discharg- 
ed. (Vs.  St.,  IX,  p.  473.)  Pincus  has  also  noticed  the  ozone  odor  in  similar  ex- 
periments with  alcohol  and  oil  (Argand)  lamps,  and  with  stearine  candles. 

Doubtless,  therefore,  we  are  justified  in  making  the  generalization  that  in  all 
cases  of  oxidation  ozone  is  formed,  and  in  many  instances  a  portion  of  it  diffuses 
into  the  atmosphere  and  escapes  immediate  combination. 


68  HOW    CROPS    FEED. 

themselves  with  this  subject.  The  most  recent  investiga- 
tions of  Daubeny,  {Journal  Chem.  JSoc,  1867,  pp.  1-28,) 
lead  to  the  conclusion  that  ozone  is  exhaled  by  plants,  a 
conclusion  previously  adopted  by  Scoutetten,  Poey,  De 
Luca,  and  Kosmann,  from  less  satisfactory  data.  Dau- 
beny  found  that  air  deprived  of  ozone  by  streaming 
through  a  solution  of  iodide  of  potassium,  then  made  to 
pass  the  foliage  of  a  plant  confined  in  a  glass  bell  and  ex- 
posed to  sunlight,  acquired  the  power  of  blueing  iodide- 
of-potassium-starch-paper,  even  when  the  latter  was  shield- 
ed from  the  light. "^  Cloez,  however,  obtained  the  contrary 
results  in  a  series  of  experiments  made  by  him  in  1855, 
(An7i.  de  Chimie  et  de  Phys.^  L,  326,)  in  which  the  oxy- 
gen, exhaled  both  from  aquatic  and  land  plants,  contained 
in  a  large  glass  vessel,  came  into  contact  with  iodide-of- 
potassium-starch-paper,  situated  in  a  narrow  and  blackened 
glass  tube.  Lawes,  Gilbert,  and  Pugh,  in  their  researches 
on  the  sources  of  the  nitrogen  of  vegetation,  {Phil.  Trans.^ 
1861)  examined  the  oxygen  evolved  from  vegetable  matter 
under  the  influence  of  strong  light,  without  finding  evidence 
of  ozone.  It  is  not  impossible  that  ozone  was  really  pro- 
duced in  the  circumstances  of  Cloez's  experiments,  but 
spent  itself  in  some  oxidizing  action  before  it  reached  the 
test-paper.  In  Daubeny's  experiments,  however,  the  more 
rapid  stream  of  air  might  have  carried  along  over  the  test- 
paper  enough  ozone  to  give  evidence  of  its  presence.  Al- 
though the  question  can  hardly  be  considered  settled,  the 
evidence  leads  to  the  belief  that  vegetation  itself  is  a 
source  of  ozone,  and  that  this  substance  is  exhaled,  to- 
gether with  ordinary  oxygen,  from  the  foliage,  when  acted 
on  by  sunlight. 

Ozone  in  the  Atmosphere,  —  Atmospheric  electricity, 
slow  oxidation,  and  combustion,  are  obvious  means  of  im- 
pregnating the  atmosphere  more  or  less  with  ozone.     If 


*  Light  alone  blues  this  paper  after  a  time  in  absence  of  ozone. 


ATMOSPHEEIC    AIR   AS    THE    FOOD    OF    PLANTS.  69 

the  oxygen  exhaled  by  plants  contains  ozone,  this  sub- 
stance miist  be  perpetually  formed  in  the  atmosphere  over 
a  large  share  of  the  earth's  surface. 

The  quantity  present  in  the  atmosphere  at  any  one  time 
must  be  very  small,  since,  from  its  strong  tendency  to  unite 
with  and  oxidize  other  substances,  it  shortly  disappears, 
and  under  most  circumstances  cannot  manifest  its  peculiar 
properties,  except  as  it  is  continually  reproduced.  The- 
ozone  present  in  any  part  of  the  atmosphere  at  any  given 
moment  is  then,  not  what  has  been  formed,  but  what  re- 
mains after  oxidable  matters  have  been  oxidized.  We  find, 
accordingly,  that  atmospheric  ozone  is  most  abundant  in 
winter;  since  then  there  not  only  occurs  the  greatest 
amount  of  electrical  excitement  ^'  in  the  atmosphere,  which 
produces  ozone,  but  the  earth  is  covered  with  snow,  and 
thus  the  oxidable  matters  of  its  surface  are  prevented 
from  consuming  the  active  oxygen. 

In  the  atmosphere  of  crowded  cities,  in  the  vicinity  of 
manure  heaps,  and  wherever  considerable  quantities  of  or- 
ganic matters  pervade  the  air,  as  revealed  by  their  odor, 
there  we  find  little  or  no  ozone.  There,  however,  it  may 
actually  be  produced  in  the  largest  quantity,  though  from 
the  excess  of  matters  which  at  once  combine  with  it,  it 
cannot  become  manifest. 

That  the  atmosphere  ordinarily  cannot  contain  more 
than  the  minutest  quantities  of  ozone,  is  evident,  if  we 
accept  the  statement  (of  Schonbein  ?)  that  it  communicates 
its  odor  distinctly  to  a  million  times  its  weight  of  air. 
The  attempts  to  estimate  the  ozone  of  the  atmosphere  give 
varying  results,  but  indicate  a  proportion  far  less  than 
sufficient  to  be  recognized  by  the  odor,  viz.,  not  more  than 
1  part  of  ozone  in  13  to  65  million  of  air.  (Zwenger, 
Pless,  and  Pierre.) 

These  figures  convey  no  just  idea  of  the  quantities  of 


*  The  amount  of  electrical  disturbance  is  not  measured  by  the  number  and 
violence  of  thunder-storms :  these  only  indicate  its  intensity. 


70  HOW    CHOPS    FEED. 

ozone  actually  produced  in  the  atmosphere  and  consumed 
in  it,  or  at  the  surface  of  the  soil.  We  have  as  yet  indeed 
no  satisfactory  means  of  information  on  this  point,  but 
may  safely  conclude  from  the  foregoing  considerations  that 
ozone  performs  an  important  part  in  1»he  economy  of 
nature. 

HelatloHS  of  Ozone  to  Vegetable  IiitritioH, — Of  the 
direct  influence  of  atmospheric  ozone  on  plants,  nothing 
is  certainly  known.  Theoretically  it  should  be  consumed 
by  them  in  various  processes  of  oxidation,  and  would  have 
ultimately  the  same  effects  that  are  produced  by  ordinary 
oxygen. 

Indirectly,  ozone  is  of  great  significance  in  our  theory 
of  vegetable  nutrition,  inasmuch  as  it  is  the  cause  of  chem- 
ical changes  which  are  of  the  highest  importance  in  main- 
taining the  life  of  plants.  This  fact  v/ill  appear  in  the 
section  on  Nitric  Acid,  which  follows. 

§8. 

COMPOUNDS  OF  NITROGEN  AND  OXYGEN  IN  THE  ATMOS- 
PHERE. 

Mtric  Acidj  ISTOgH. — Under  the  more  common  name 
Aqua  fortis  (strong  water)  this  highly  important  sub- 
stance is  to  be  found  in  every  apothecary  shop.  It  is, 
when  pure,  a  colorless,  usually  a  yellow  liquid,  whose 
most  obvious  properties  are  its  sour,  burning  taste,  and 
power  of  dissolving,  or  acting  upon,  many  metals  and  other 
bodies. 

When  pure,  it  is  a  half  heavier  than  its  own  bulk  of 
water,  and  emits  pungent,  suffocating  vapors  or  fumes ;  in 
this  state  it  is  rarely  seen,  being  in  general  mixed  or  di- 
luted with  more  or  less  water ;  when  very  dilute,  it  evolves 
no  fumes,  and  is  even  pleasant  to  the  taste. 

It  has  the  properties  of  an  acid  in  the  most  eminent  de- 
gree;   vegetable  blue  colors  are  reddened  by  it,  and  it 


ATMOSPHEEIC    AIPw   AS   THE   FOOD    OF   PLANTS.  71 

unites  with  great  avidity  to  all  basic  bodies,  forming  a 
long  list  of  nitrates. 

It  is  volatile,  and  evaporates  on  exposure  to  air,  though 
not  so  rapidly  as  water. 

Nitric  acid  has  a  strong  affinity  for  water ;  hence  its 
vapors,  Avhen  they  escape  into  moist  air,  condense  the 
moisture,  making  therewith  a  visible  cloud  or  fume.  For 
the  same  reason  the  commercial  acid  is  always  more  or  less 
dilute,  it  being  difficult  or  costly  to  remove  the  water  en- 
tirely. 

I^itric  acid,  as  it  occurs  in  commerce,  is  made  by  heat- 
ing together  sulphuric  acid  and  nitrate  of  soda,  when 
nitric  acid  distils  off,  and  sulphate  of  soda  remains  behind. 

Nitrate  of       Sulphuric     Bisulphate  of         Nitric 

soda.  acid.  soda.  acid. 

N03Na     +     H^SO,     =     HNa  SO^     +     l^O^H     _ 

Nitrate  of  soda  is  formed  in  nature,  and  exists  in  im- 
mense accumulations  in  the  southern  part  of  Peru,  (see 
p.  252.) 

AttliyclroMS  i\itric  Acidl,  N2O5,  is  what  is  commonly  under- 
stood as  existing  in  combination  witli  bases  in  the  nitrates.  It  is  a 
crystallized  body,  but  is  not  an  acid  until  it  unites  with  the  elements  of 
water. 

Mtrate  of  Ammonia,  NH3  NOgH,  or  NH^  ^03,  may 
be  easily  prepared  by  adding  to  nitric  acid,  ammonia  in 
slight  excess,  and  evaporating  the  solution.  The  salt  read- 
ily crystallizes  in  long,  flexible  needles,  or  as  a  fibrous 
mass.  It  gathers  moisture  from  the  air,  and  dissolves  in 
about  half  its  weight  of  water. 

If  nitrate  of  ammonia  be  mixed  with  potash,  soda,  or 
lime,  or  with  the  carbonates  of  these  bases,  an  exchange 
of  acids  and  bases  takes  place,  the  result  of  which  is  ni- 
trate of  potash,  soda,  or  lime,  on  the  one  hand,  and  free 
ammonia  or  carbonate  of  ammonia  on  the  other. 

Nitrons  Oxide,  N2O,— When  nitrate  of  ammonia  is  heated,  it 


72  HOW    CEOPS    FEED. 

melts,   and  gradually  decomposes  iuto  water  and  nitrous  oxide,   or 
"  laughing;  gas,"  as  represented  by  the  equation : — 
NH4  NO3    =    2  H2O     +     N2O 

ISTitric  acid  and  the  nitrates  act  as  powerful  oxidizing 
agents,  i.  e.,  they  readily  yield  up  a  portion  or  all  tlieir 
oxygen  to  substances  having  strong  affinities  for  this  ele- 
ment. If,  for  example,  charcoal  be  warmed  with  strong 
nitric  acid,  it  is  rapidly  acted  upon  and  converted  into 
carbonic  acid.  If  thrown  into  melted  nitrate  of  soda  or 
saltpeter,  it  takes  fire,  and  is  violently  burned  to  carbonic 
acid.  Similarly,  sulphur,  phosphorus,  and  most  of  the 
metals,  may  be  oxidized  by  this  acid. 

When  nitric  acid  oxidizes  other  substances,  it  itself  losed 
oxygen  and  suffers  reduction  to  compounds  of  nitrogen, 
containing  less  oxygen.  Some  of  these  compounds  require 
notice. 

Nitric  Oxide,  NO. — ^When  nitric  acid  somewhat  diluted 
with  water  acts  upon  metallic  copper,  a  gas  is  evolved, 
which,  after  washing  with  water,  is  colorless  and  permanent. 
It  is  nitric  oxide.  By  exposure  to  air  it  unites  with  oxy- 
gen, and  forms  red,  suffocating  fumes  of  nitric  peroxide, 
or,  if  the  oxygen  be  not  in  excess,  nitrous  acid  is  formed. 

Nitric  Peroxide,  (hyponitric  acid,)  ISTO^,  appears  as  a 
dark  yellowish-red  gas  when  strong  nitric  acid  is  poured 
upon  copper  or  tin  exposed  to  the  air.  It  is  procured  in 
a  state  of  purity  by  strongly  heating  nitrate  of  lead :  by 
a  cold  approaching  zero  of  Fahrenheit's  thermometer,  it 
may  be  condensed  to  a  yellow  liquid  or  even  solid. 

Nitrous  Acid,  (anhydrous,)  N^Og,  is  produced  when 
nitric  peroxide  is  mixed  with  water  at  a  low  temperature, 
nitric  acid  being  formed  at  the  same  time. 

Nitric  peroxide.    Water.       Nitric  acid.  -^^^^^'^  ^^'^^^^' 
^  aiiriydrous. 

4  :Nro,   +   HP   =   2  NHO3   +   -^^  O3 

It  may  be  procured  as  a  blue  liquid,  which  boils  at  the 
freezing  point  of  water. 


ATMOSPHERIC    AIH    AS   THE    FOOD    OF    PLANTS.  73 

When  nitric  peroxide  is  put  in  contact  with  sohitions 
of  an  alkali,  there  results  a  mixture  of  nitrate  and  nitrite 
of  the  alkali. 

Nitria      Hydrate  of  Nitrate  of  Nitrite  of     jn- 
peroxide.        potash.         potash.        potash.  ^^' 

2  NO,    +    2HK0    =    NKO3    +    ISTKO,    +    H^  O 

Nitrite  of  Ammonia,  NH^  1^0,  is  known  to  the  chem- 
ist as  a  white  crystalline  solid,  very  soluble  in  water. 
When  its  concentrated  aqueous  solution  is  gently  heated, 
the  salt  is  gradually  resolved  into  water  and  nitrogen  gas. 
This  decomposition  is  represented  by  the  following  equa- 
tion : 

NH,  :tTO,     =     21{fi     +     21^ 

This  decomposition  is,  however,  not  complete.  A  por- 
tion of  ammonia  escapes  in  the  vapors,  and  nitrous  acid 
accumulates  in  the  residual  liquid.  (Pettenkofer.)  Addi- 
tion of  a  strong  acid  facilitates  decomposition ;  an  alkali 
retards  it.  When  a  dilute  solution,  1  :  500,  is  boiled,  but 
a  small  portion  of  the  salt  is  decomposed,  and  a  part  of  it 
is  found  in  the  distillate.  Very  dilute  solutions,  1  :  100,000, 
may  be  boiled  without  suffering  any  alteration  whatever. 
(Schoyen.) 

Schonbein  and  others  have  (erroneously  ?)  supposed  that 
nitrite  of  ammonia  is  generated  by  the  direct  union  of 
nitrogen  and  water.  Nitrite  of  ammonia  may  exist  in  the 
atmosphere  in  minute  quantity. 

Nit7'ites  of  potash  and  soda  may  be  procured  by  strongly 
heating  the  corresponding  nitrates,  whereby  oxygen  gas  is 
expelled. 

The  Mutual  Coavertibility  of  Nitrates  and  Nitrites  is 

illustrated  by  various  statements  already  made.  There 
are,  in  fact,  numerous  substances  which  reduce  nitrates  to 
nitrites.  According  to  Schonbein,  {Jour.  PraJct.  Ch.^  84, 
207,)  this  reducing  effect  is  exercised  by  the  albuminoids, 
by  starch,  glucose,  and  milk-sugar,  but  not  by  cane-sugar. 
4 


74  HOW    CROPS    FEED. 

It  is  also  manifested  by  many  metals,  as  zinc,  iron,  and 
lead,  and  by  any  mixture  evolving  hydrogen,  as,  for  ex- 
ample, putrefying  organic  matter.  On  the  other  hand, 
ozone  instantly  oxidizes  nitrites  to  nitrates. 

Eediiciioii  of  Nitrates  and  Nitrites  to  AmMonia. — 
Some  of  the  substances  which  convert  nitrates  into  nitrites 
may  also  by  their  prolonged  action  transform  the  latter 
into  ammonia.  When  small  fragments  of  zinc  and  iron 
mixed  together  are  drenched  with  warm  solution  of  caustic 
potash,  hydrogen  is  copiously  disengaged.  If  a  nitrate  be 
added  to  the  mixture,  it  is  at  once  reduced,  and  ammonia 
escapes.  If  to  a  mixture  of  zinc  or  iron  and  dilute  chlor- 
hydric  acid,  such  as  is  employed  in  preparing  hydrogen 
gas,  nitric  acid,  or  any  nitrate  or  nitrite  be  added,  the 
evolution  of  hydrogen  ceases,  or  is  checked,  and  ammonia 
is  formed  in  the  solution,  whence  it  can  be  expelled  by 
lime  or  potash. 

Witric  acid.     Hydrogen.     Ammonia.  Water. 

NO3H       +       8H       =       -^11,       +       3H,0 

The  appearance  of  nitrous  acid  in  this  process  is  an  in- 
termediate step  of  the  reduction. 

Fiirtlier  Ilediictioa  ©f  Mtric  and  Nitrons  Acids. — Un- 
der certain  conditions  nitric  acid  and  nitrous  acid  are  still 
further  deoxidized.  Kesbit,  who  first  employed  the  reduc- 
tion of  nitric  acid  to  ammonia  by  means  of  zinc  and  dilute 
chlorhydric  acid  as  a  means  of  determining  the  quantity 
of  the  former,  mentions  {Quart.  Jour.  Chem.  Soe.,  1847, 
p.  283,)  that  when  the  temperature  of  the  liquid  is  allowed  1 
to  rise  somewhat,  nitric  oxide  gas,  ISTO,  escapes. 

From  weak  nitric  acid,  zinc  causes  the  evolution  of  ni- 
trous oxide  gas,  IST^O. 

As  already  mentioned,  nitrate  of  ammonia,  when  heated 
to  fusion,  evolves  nitrous  oxide,  l^fi.  Emmet  showed 
that  by  immersing  a  strip  of  zinc  in  the  melted  salt,  nearly 
pure  nitrogen  gas  is  set  free. 


ATMOSPHEEIC    AIR    AS    THE    FOOD    OF   PLANTS.  75 

When  nitric  acid  is  heated  with  lean  flesh  (fibrin),  nitric 
oxide  and  nitrogen  gases  both  appear.  It  is  thus  seen 
that  by  successive  steps  of  deoxidation  nitric  acid  may 
be  gradually  reduced  to  nitrous  acid,  ammonia,  nitric  oxide, 
nitrous  oxide,  and  finally  to  nitrogen. 

Tests  for  Nitric  and  r^'itroaas  Acids.  — The  fact  that 
these  substances  often  occur  in  extremely  minute  quantities  reuders  it 
needful  to  employ  yery  delicate  tests  for  their  recognition. 

Price's  Test. — Free  nitrous  acid  decomposes  iodide  of  potassium  in  the 
same  manner  as  ozone,  and  hence  gives  a  blue  color,  with  a  mixture  of 
this  salt  and  starch-paste.  Any  nitrite  produces  the  same  effect  if  to 
the  mixture  dilute  sulphuric  acid  be  added  to  liberate  the  nitrous  acid. 
Pure  nitric  acid,  if  moderately  dilute,  and  dilute  solutions  of  nitrates 
mixed  with  dilute  sulphuric  acid,  are  without  immediate  effect  upon 
iodide-of-potassium-starch-paste.  If  the  solution  of  a  nitrate  be  min- 
gled with  dilute  sulphuric  acid,  and  agitated  for  some  time  with  zinc 
filings,  reduction  to  nitrite  occurs,  and  then  addition  of  the  starch-paste, 
etc.,  gives  the  blue  coloration.  According  to  Schonbein,  this  test,  first 
proposed  by  Price,  will  detect  nitrous  acid  when  mixed  with  one-huud- 
red-thousand  times  its  weight  of  water.  It  is  of  course  only  applicable 
in  the  absence  of  other  oxidizing  agents. 

Green  Vitriol  Test. — A  very  characteristic  test  for  nitric  and  nitrous 
acids,  and  a  delicate  one,  though  less  sensitive  than  that  just  describ- 
ed, is  furnished  by  common  green  vitriol,  or  protosulphate  of  iron. 
Nitric  oxide,  the  red  gas  which  is  evolved  from  nitric  acid  or  nitrates  by 
mixing  them  with  excess  of  strong  sulphuric  acid,  and  from  nitrous  acid 
or  nitrites  by  addition  of  dilute  sulphuric  acid,  gives  with  green  vitriol  a 
peculiar  blackish-brown  coloration.  To  test  for  minute  quantities  of 
nitrous  acid,  mix  the  solution  with  dilute  sulphuric  acid  and  cautiously 
pour  this  liquid  upon  an  equal  bulk  of  cold  saturated  solution  of  green 
vitriol,  so  that  the  former  liquid  floats  upon  the  latter  without  mingling 
much  with  it.  On  standing,  the  coloration  will  be  perceived  where  the 
two  liquids  are  in  contact. 

Nitric  acid  is  tested  as  follows :  Mix  the  solution  of  nitrate  with  an 
equal  volume  of  concentrated  sulphuric  acid ;  let  the  mixture  cool,  and 
pour  upon  it  the  solution  of  green  vitriol.  The  coloration  will  appear 
between  the  two  liquids. 

Formation  of  Nitrogen  Compounds  in  the  Atmosphere. 

— a.  From  free  nitrogen,  by  electrical  ozone.  Schonbein 
and  Meissner  have  demonstrated  that  a  discharge  of  elec- 
tricity through  air  in  its  ordinary  state  of  dryness  causes 
oxygen  and  nitrogen  to  unite,  with  the  formation  of  nitric 
peroxide,  NO^.     Meissner  has  proved  that  not  the  elec- 


76  HOW    CROPS    FEED. 

tricity  directly,  but  the  ozone  developed  by  it,  accom- 
plishes this  oxidation.  It  has  long  been  known  that  nitric 
peroxide  decomposes  with  water,  yielding  nitric  and  ni- 
trous acids  thus : 

2  NO,     +     H,0     =     NO3H     +     NO^H. 

It  is  further  known  that  nitrous  acid,  both  in  the  free 
state  and  in  combination,  is  instantly  oxidized  to  nitric 
acid  by  contact  with  ozone. 

Tlius  is  explained  the  ancient  observation,  first  made  by 
Cavendish  in  1784,  that  when  electrical  sparks  are  trans- 
mitted through  moist  air,  confined  over  solution  of  potash, 
nitrate  of  potash  is  formed.  (For  information  regarding 
this  salt,  see  p.  252.) 

Until  recently,  it  has  been  supposed  that  nitric  acid  is 
present  in  only  those  rains  which  accompany  thunder- 
storms. 

It  appears,  however,  from  the  analyses  of  both  Way  and 
Boussingault,  that  visible  or  audible  electric  discharges 
do  not  perceptibly  influence  the  proportion  of  nitric  acid 
in  the  air ;  the  rains  accompanying  thunder-storms  not 
being  always  nor  usually  richer  in  this  substance  than 
others. 

Yon  Babo  and  Meissner  have  demonstrated  that  silent 
electrical  discharges  develop  more  ozone  than  flashes  of 
lightning.  Meissner  has  shown  that  the  electric  spark 
causes  the  copious  formation  of  nitric  peroxide  in  its  im- 
mediate path  by  virtue  of  the  heat  it  excites,  which  in- 
creases the  energy  of  the  ozone  simultaneously  produced, 
and  causes  it  to  expend  itself  at  once  in  the  oxidation  of 
nitrogen.  Boussingault  informs  us  that  in  some  of  the 
tropical  regions  of  South  America  audible  electrical  dis- 
charges are  continually  taking  place  throughout  the  whole 
year.  In  our  latitudes  electrical  disturbance  is  perpetu- 
ally occurring,  but  equalizes  itself  mostly  by  silent  dis- 
charge. The  ozone  thus  noiselessly  developed,  though 
operating  at  a  lower  temperature,  and   therefore  more 


ATMOSPHERIC   AIR    AS   THE    FOOD    OF    PLANTS.  77 

slowly  than  that  which  is  produced  by  lightning,  must 
really  oxidize  much  more  nitrogen  to  nitric  acid  than  the 
latter,  because  its  action  never  ceases. 

Formation  of  Mtrogea  Compounds  in  tSie  Atmosphere. 

— 5.  From  free  nitrogen  (by  ozone  ?)  in  the  processes  of 
combustion  and  slow  oxidation. 

At  high  temperatures. — Saussure  first  observed  {^Aim. 
de  Chimie^  Ixxi,  282),  that  in  the  burning  of  a  mixture  of 
oxygen  and  hydrogen  gases  in  the  air,  the  resulting  water 
contains  ammonia.  He  had  previously  noticed  that  nitric 
acid  and  nitrous  acid  are  formed  in  the  same  process. 

Kolbe  {Ann.  Chem.  u.  Pharm.^  cxix,  176)  found  that 
when  a  jet  of  burning  hydrogen  was  passed  into  the  neck 
of  an  open  bottle  containing  oxygen,  reddish-yellow  va- 
pors of  nitrous  acid  or  nitric  peroxide  were  copiously  j^ro- 
duced  on  atmospheric  air  becoming  mingled  with  the 
burning  gases. 

Bence  Jones  {Phil.  Trans.,  1851,  ii,  399)  discovered  ni- 
tric (nitrous  ?)  acid  in  the  water  resulting  from  the  burn- 
ing of  alcohol,  hydrogen,  coal,  wax,  and  i:)urified  coal-gas. 

By  the  use  of  the  iodide-of-potassium-starch  test  (Price's 
test),  Boettger  {Jour,  far  PraJct.  Chem.,  Ixxxv,  396)  and 
Schonbein  (ibid.,  Ixxxiv,  215)  have  more  recently  confirm- 
ed the  result  of  Jones,  but  because  they  could  detect 
neither  free  acid  nor  free  alkali  by  the  ordinary  test-pa- 
pers, they  concluded  that  nitrous  acid  and  ammonia  are 
simultaneously  formed,  that,  in  fact,  nitrite  of  ammonia 
is  generated  in  all  cases  of  rapid  combustion. 
•  Meissner  ( JJntersuchimgen  ilher  den  Sauerstoff,  1863,  p. 
283)  was  unable  to  satisfy  himself  that  either  nitrous  acid 
or  ammonia  is  generated  in  combustion. 

Finally,  Zabelin  {Ann.  Chem.  u.  Ph.,  cxxx,  54)  in  a 
series  of  careful  experiments,  found  that  when  alcohol,  il- 
luminating gas,  and  hydrogen,  burn  in  the  air,  nitrous  acid 
and  ammonia  are  very  frequently,  but  not  always,  formed. 


78  HOW    CROPS    FEED. 

When  the  combustion  is  so  perfect  that  the  resulting  wa- 
ter is  colorless  |and  pure,  only  nitrous  acid  is  formed ; 
when,  on  the  other  hand,  a  trace  of  organic  matters  es- 
capes oxidation,  less  or  no  nitrous  acid,  but  in  its  place 
ammonia,  appears  in  the  water,  and  this  under  circum- 
stances that  preclude  its  absorption  from  the  atmosphere. 

Zabelin  gives  no  proof  that  the  combustibles  he  em- 
ployed were  absolutely  free  from  compounds  of  nitrogen, 
but  otherwise,  his  experiments  are  not  oj)en  to  criticism. 

Meissner's  observations  were  indeed  made  under  some- 
what different  conditions ;  but  his  negative  results  Avere 
not  improbably  arrived  at  simply  because  he  employed  a 
much  less  delicate  test  for  nitrous  acid  than  was  used  by 
Schonbein,  Boettger,  Jones,  and  Zabehn.* 

We  must  conclude,  then,  that  nitrous  acid  and  ammonia 
are  usually  formed  from  atmospheric  nitrogen  during  rap- 
id combustion  of  hydrogen  and  compounds  of  hydrogen 
and  carbon.  The  quantity  of  these  bodies  thus  generated 
is,  however,  in  general  so  extremely  small  as  to  require  the 
most  sensitive  reagents  for  their  detection. 

At  low  temperatures. — Schonbein  was  the  first  to  observe 
that  nitric  acid  may  be  formed  at  moderately  elevated  or 
even  ordinary  temperatures.  He  obtained  several  grams 
of  nitrate  of  potash  by  adding  carbonate  of  potash  to  the 
liquid  resulting  from  the  slow  oxidation  of  phosphorus  in 
the  preparation  of  ozone. 

More  recently  he  believed  to  haA^e  discovered  that  ni- 
trogen compounds  are  formed  by  the  simple  evaporation 
of  water.     He  heated  a  vessel  (which  was  indifferently  of 


*  Meissner  rejected  Price's  test  in  the  belief  that  it  cannot  serve  to  distinguish 
nitrous  acid  from  peroxide  of  hydrogen,  H2  O2.  He  therefore  made  the  liquid 
to  be  examined  alkaline  with  a  slight  excess  of  potash,  concentrated  to  small 
bulk  and  tested  with  dilute  sulphuric  acid  and  protosulphate  of  iron.  (JJnters. 
il.  d.  Saiie7'stoff,  p.  233).  Schonbein  had  found  that  iodide  of  potassium  is  decom- 
posed after  a  little  time  by  concentrated  solutions  of  peroxide  of  hydrogen,  but  is 
unaffected  by  this  body  when  dilute,  (Jour,  fur  2'>rakt.  Chetn.,  Ixxxvi,  p.  90). 
Zabelin  agrees  with  Schonbein  that  Price's  test  is  decisive  between  peroxide  of 
hydrogen  and  nitrous  acid.    {Ann.  Cliem,  u.  Ph.,  cxxx,  p.  58.) 


ATMOSPHESIC    AIR    AS    THE    FOOD    OE   PLAISTTS.  79 

glass,  porcelain,  silver,  etc.,)  so  that  water  would  evapo- 
rate rapidly  from  its  surface.  The  purest  water  was  then 
dropped  into  the  warm  dish  in  small  quantities  at  a  time, 
each  portion  being  allowed  to  evaporate  away  before  the 
next  was  added.  Over  the  vapor  thus  generated  was  held 
the  mouth  of  a  cold  bottle  until  a  portion  of  the  vapor 
was  condensed  in  the  latter. 

The  water  thus  collected  gave  the  reactions  for  nitrous 
acid  and  ammonia,  sometimes  quite  intensely,  again  faint- 
ly, and  sometimes  not  at  all. 

By  simply  exposing  a  piece  of  filter-paper  for  a  suffi- 
cient time  to  the  vapors  arising  from  pure  water  heated 
to  boiling,  and  pouring  a  few  drops  of  acidified  iodide-of- 
potassium-starch-paste  upon  it,  the  reaction  of  nitrous  acid 
was  obtained.  When  paper  which  had  been  impregnated 
with  dilute  solution  of  pure  potash  was  hung  in  the  va- 
pors that  arose  from  water  heated  in  an  open  dish  to  100° 
F.,  it  shortly  acquired  so  much  nitrite  of  potash  as  to  re- 
act with  the  above  named  test. 

Lastly,  nitrous  acid  and  ammonia  appeared  when  a 
sheet  of  filter-paper,  or  a  piece  of  linen  cloth,  which  had 
been  moistened  with  the  purest  water,  was  allowed  to  dry 
at  ordinary  temperatures,  in  the  open  air  or  in  a  closed 
vessel.  {Jour,  far  Frakt,  Chem.^  Ixvi,  131.)  These  ex- 
periments of  Schonbein  are  open  to  criticism,  and  do  not 
furnish  perfectly  satisfactory  evidence  that  nitrous  acid 
and  ammonia  are  generated  under  the  circumstances  men- 
tioned. Bohlig  has  objected  that  these  bodies  might  be 
gathered  from  the  atmosphere,  where  they  certainly  exist, 
though  in  extremely  minute  quantity. 

Zabelin,  in  the  paper  before  referred  to  {Ami,  Ch.  Ph.^ 
cxxx,  p.  76),  communicates  some  experimental  results' 
which,  in  the  writer's  opinion,  serve  to  clear  up  the  mat- 
ter satisfactorily. 

Zabelin  ascertained  in  the  first  place  that  the  atmos- 
pheric air  contained  too  little  ammonia  to  influence  ISTess- 


80  now    CROPS    FEED. 

ler's  test,'"''  which  is  of  extreme  delicacy,  and  whicli  he  con- 
stantly employed  in  his  investigations. 

Zabelin  operated  in  closed  vessels.  The  apparatus  he 
used  consisted  of  two  glass  flasks,  a  larger  and  a  smaller 
one,  winch  were  closed  by  corks  and  fitted  with  glass 
tubes,  so  that  a  stream  of  air  entering  the  larger  vessel 
should  bubble  through  water  covering  its  bottom,  and 
thence  passing  into  the  smaller  flask  should  stream  through 
Nessler's  test.  Next,  he  found  that  no  ammonia  and 
(by  Price's  test)  but  doubtful  traces  of  nitrous  acid  could 
be  detected  in  the  purest  water  when  distilled  alone  in 
this  apparatus. 

Zabelin  likewise  showed  that  cellulose  (clippings  of  filter- 
paper  or  shreds  of  linen)  yielded  no  ammonia  to  Nessler's 
test  when  heated  in  a  current  of  air  at  temperatures  of 
120°  to  160°  F. 

Lastly,  he  found  that  when  cellulose  and  pure  water  to- 
gether were  exposed  to  a  current  of  air  at  the  tempera- 
tures just  named,  ammonia  was  at  once  indicated  by 
Nessler's  test.  Nitrous  acid,  however,  could  be  detected, 
if  at  nil,  in  the  minutest  traces  only. 

Views  of  Schdnbein. — The  reader  should  observe  that 
Boettger  and  Schonbein,  finding  in  the  first  instance  by 
the  exceedingly  sensitive  test  with  iodide  of  potassium 
and  starch-paste,  that  nitrous  acid  was  formed,  when  hy- 
drogen burned  in  the  air,  while  the  water  thus  generated 
was  neutral  in  its  reaction  with  the  vastly  less  seiisitive 
litmus  test-paper,  concluded  that  the  nitrous  acid  was 
united  -with  some  base  in  the  form  of  a  neutral  salt.  Af- 
terward, the  detection  of  ammonia  appeared  to  demon- 
strate the  formation  of  nitrite  of  ammonia. 

We  have  already  seen  that  nitrite  of  ammonia,  by  ex- 
posure to  a  moderate  heat,  is  resolved  into  nitrogen  and 
water.     Schonbein  assumed  that  under  the  conditions  of 


*  See  p.  54. 


ATMOSPHERIC    AIR    AS   THE    FOOD    OF   PLAJSTTS.  81 

his  experiments   nitrogen  and  Avater  combine  to  form  ni- 
trite of  ammonia. 

2N     +     2  HP     =     NH3,  jN^O^H 

This  theory,  supported  by  the  authority  of  so  distin- 
guished a  philosopher,  has  been  almost  universally  credit- 
ed.* It  has,  however,  little  to  warrant  it,  even  in  the  way 
of  probability.  If  traces  of  nitrite  of  ammonia  can  be 
produced  by  the  immediate  combination  of  these  excep- 
tionally abundant  and  universally  diffused  bodies  at  com- 
mon temperatures,  or  at  the  boiling  point  of  water,  or 
lastly  in  close  proximity  to  the  flames  of  burning  gases, 
then  it  is  simply  inconceivable  that  a  good  share  of  the 
atmosphere  should  not  speedily  dissolve  in  the  ocean,  for 
the  conditions  of  Schonbein's  experiments  prevail  at  all 
times  and  at  all  places,  so  far  as  these  substances  are  con* 
cerned. 

The  discovery  of  Zabelin  that  ammonia  and  nitrous  acid 
do  not  always  appear  in  equivalent  quantities  or  even 
simultaneously,  while  difficult  to  reconcile  with  Schon- 
bein's theory,  in  no  wise  conflicts  with  any  of  his  facts. 
A  quantity  of  free  nitrous  acid  that  admits  of  recognition 
by  help  of  Price's  test  would  not  necessarily  have  any 
effect  on  litmus  or  other  test  for  free  acids.  There  re- 
mains, then,  no  necessity  of  assuming  the  generation  of  ni- 
trite of  ammonia,  and  the  fact  of  the  separate  appearance 
of  the  elements  of  this  salt  demands  another  explanation. 

The  Author's  Opinion. — The  writer  is  not  able,  perhaps, 
to  offer  a  fully  satisfactory  explanation  of  the  facts  above 
adduced.  He  submits,  however,  some  speculations  which 
appear  to  him  entirely  warranted  by  the  present  aspects 
of  the  case,  in  the  hope  that  some  one  with  the  time  at 


*  Zabelin  was  inclined  to  believe  that  his  failure  to  detect  nitrous  acid  in  some 
of  his  experiments  where  organic  matters  intervened,  was  due  to  a  power  pos- 
sessed by  these  organic  matters  to  mask  or  impair  the  delicacy  of  Price's  test, 
as  first  noticed  by  Pettenkofer  and  since  demonstrated  by  Schoubein  in  case  of 
urine. 

4* 


82  uo^Y  CEOPS  feed. 

command  for  experimental  study,  will  establish  or  disprove 
them  by  suitable  investigations. 

He  believes,  from  the  existing  evidence,  that  free  nitro- 
gen can,  in  no  case,  unite  directly  with  water,  but  in  the 
conditions  of  all  the  foregoing  experiments,  it  enters  com- 
bination by  the  action  of  ozone,  as  Schonbein  formerly 
maintained  and  was  the  first  to  suggest. 

We  have  already  recounted  the  evidence  that  goes  to. 
show  the  formation  of  ozone  in  all  cases  of  oxidation,  both 
at  high  and  low  temperatures,  p.  67. 

In  Zabelin's  experiments  we  may  suppose  that  ozone 
was  formed  by  the  oxidation  of  the  cellulose  (linen  and 
paper)  he  employed.  In  Schonbein's  experiments,  where 
paper  or  linen  was  not  employed,  the  dust  of  the  air  may 
have  supplied  the  organic  matters. 

The  first  result  of  the  oxidation  of  nitrogen  is  nitrous 
acid  alone  (at  least  Schonbein  and  Bohlig  detected  no  ni- 
tric acid),  when  the  combustion  is  complete,  as  in  case  of 
hydrogen,  or  when  organic  matters  are  excluded  from  the 
experiment.  Nitric  acid  is  a  product  of  the  subsequent 
oxidation  of  nitrous  acid.  When  organic  matters  exist  in 
the  product  of  combustion,  as  when  alcohol  burns  in  a 
heated  apparatus  yielding  water  having  a  yellowish  color, 
it  is  probable  that  nitrous  acid  is  formed,  but  is  afterward 
reduced  to  ammonia,  as  has  been  already  explained,  p.  74. 

Zabelin,  in  the  article  before  cited,  refers  to  Schonbein 
as  authority  for  the  fact  that  various  organic  bodies,  viz., 
all  the  vegetable  and  animal  albuminoids,  gelatine,  and 
most  of  the  carbohydrates,  especially  starch,  glucose,  and 
milk-sugar,  reduce  nitrites  to  am/iniionia,  and  ultimately  to 
nitrogen ;  and  although  we  have  not  been  able  to  find  such 
a  statement  in  those  of  Schonbein's  papers  to  which  we 
have  had  access,  it  is  entirely  credible  and  in  accordance 
with  numerous  analogies. 

If,  as  thus  appears  extremely  probable,  ozone  is  devel- 
oped in  all  cases  of  oxidation,  both  rapid  and  slow,  then 


ATMOSPIIEKIC    Air.    AS    THE    FOOD    OE    PLAXTS.  83 

every  flame  and  fire,  every  decaying  plant  and  animal, 
the  organic  matters  that  exhale  from  the  skin  and  lungs 
of  living  animals,  or  from  the  foliage  and  flowers  of  plants, 
especially,  perhaps,  the  volatile  oils  of  cone-bearing  trees, 
are,  indirectly,  means  of  converting  a  portion  of  free  ni- 
trogen into  nitrous  and  nitric  acids,  or  ammonia. 

These  topics  will  be  recurred  to  in  our  discussion  of 
Nitrification  in  the  Soil,  p.  254. 

Formatios  of  Mtrogen  CompoMnds  m  the  Atmospliere. 
— c.  From  free  nitrogen  by  ozone  accompanying  the  oxy- 
gen exhaled  from  green  foliage  in  sunlight,    ■ 

The  evidence  upon  the  question  of  the  emission  of  ozone 
by  plants,  or  of  its  formation  in  the  vicinity  of  foliage,  has 
been  briefly  presented  on  page  68.  The  present  state  of 
investigation  does  not  permit  us  to  pronounce  definitely 
upon  this  point.  There  are,  however,  some  facts  of  agri- 
culture which,  perhaps,  find  their  best  explanation  by  as- 
suming this  evolution  of  ozone. 

It  has  long  been  known  that  certain  crops  are  especially 
aided  in  their  growth  by  nitrogenous  fertilizers,  while  oth- 
ers are  comparatively  indifferent  to  them.  Thus  the  cereal 
grains  and  grasses  are  most  frequently  benefited  by  appli- 
cations of  nitrate  of  soda,  Peruvian  guano,  dung  of  ani- 
mals, fish,  flesh  and  blood  manures,  or  other  matters  rich 
in  nitrogen.  On  the  other  hand,  clover  and  turnips  flour- 
ish best,  as  a  rule,  when  treated  with  phosphates  and  alka- 
line substances,  and  are  not  manured  with  animal  fertiliz- 
ers so  economically  as  the  cereals.  It  has,  in  fact,  become 
a  rule  of  practice  in  some  of  the  best  farming  districts  of 
England,  where  systematic  rotation  of  crops  is  followed, 
to  apply  nitrogenous  manures  to  the  cereals  and  phos- 
phates to  turnips.  Again,  it  is  a  fact,  that  whereas  nitro- 
genous manures  are  often  necessary  to  produce  a  good 
wheat  crop,  in  which,  at  30  bu.  of  grain  and  2,600  lbs.  of 
straw,  there  is  contained  45  lbs.  of  nitrogen ;  a  crop  of 
clover  may  be  produced  without  nitrogenous  manure,  in 


84  '  HOAY    CROPS    FEED. 

whidi  would  be  taken  from  the  field  twice  or  thrice  the 
above  amount  of  nitrogen,  although  the  period  of  growth 
of  the  two  crops  is  about  the  same.  Ulbricht  found  in 
his  investigation  of  the  clover  plant  {Vs.  St.,  TV.,  p.  27) 
that  the  soil  appears  to  have  but  little  influence  on  the 
content  of  nitrogen  of  clover,  or  of  its  individual  organs. 
These  facts  admit  of  another  expression,  viz. :  Clover, 
though  containing  two  or  three  times  more  nitrogen,  and 
requiring  correspondingly  larger  supplies  of  nitrates  and 
ammonia  than  wheat,  is  cible  to  supply  itself  mucli  more 
easily  than  the  latter  crop.  In  parts  of  the  Genesee  wheat 
region,  it  is  the  custom  to  alternate  clover  with  wheat,  be- 
cause the  decay- of  the  clover  stubble  and  roots  admirably 
prepares  the  ground  for  the  last-named  crop.  The  same 
preparation  might  be  had  by  the  more  expensive  process 
of  dressing  with  a  highly  nitrogenous  manure,  and  it  is 
scarcely  to  be  doubted  that  it  is  the  nitrogen  gathered  by 
the  clover  which  insures  the  wheat  crop  that  follows.  It 
thus  appears  that  the  plant  itself  causes  the  formation  in 
its  neigliborhood  of  assimilable  compounds  of  nitrogen, 
and  that  some  plants  excel  others  in  their  power  of  accom- 
plishing this  important  result. 

On  the  supposition  that  ozone  is  emitted  by  plants,  it  is 
plain  that  those  crops  which  produce  the  largest  mass  of 
foliage  develop  it  most  abundantly.  By  the  action  of 
this  ozone,  the  nitrogen  that  bathes  the  leaves  is  convert- 
ed into  nitric  acid,  which,  in  its  turn,  is  absorbed  by  the 
plant.  The  foliage  of  clover,  cut  green,  and  of  root  crops, 
maintains  its  activity  until  the  time  the  crop  is  gathered ; 
Jie  supply  of  nitrates  thus  keeps  pace  with  the  wants  of 
the  plant.  In  case  of  grain  crops,  the  functions  of  the  fo- 
liage decline  as  the  seed  begins  to  develop,  and  the  plant's 
means  of  providing  itself  with  assimilable  nitrogen  fail, 
although  the  need  for  it  still  exists.  Furthermore,  the 
clover  cut  for  hay,  leaves  behind  much  more  roots  and 
stubble  per  acre  than  grain  crops,  and  the  clover  stubble 


ATMOSPHERIC   AIE   AS   THE  FOOD    OF   PLANTS,  85 

is  twice  as  rich  in  nitrogen  as  the  stubble  of  ripened  grain. 
This  is  a  result  of  the  fact  that  the  clover  is  cut  when  in 
active  growth,  while  the  grain  is  harvested  after  the  roots, 
stems,  and  leaves,  have  been  exhausted  of  their  own  juices 
to  meet  the  demands  of  the  seed. 

Whatever  may  be  the  value  of  our  explanations,  the 
fact  is  not  to  be  denied  that  the  soil  is  enriched  in  nitrogen 
by  the  culture  of  large-leaved  plants,  which  are  harvested 
wlnle  in  active  growth,  and  leave  a  considerable  propor- 
tion of  roots,  leaves,  or  stubble,  on  the  field.  On  the  other 
hand,  the  field  is  impoverished  in  nitrogen  when  grain 
crops  are  raised  upon  it. 

Formation  of  Nitric  Acid  from  Ammonia. — Ammonia 
(carbonate  of  ammonia)  under  the  influence  of  ozone  is 
converted  into  nitrate  of  ammonia,  (Baumert,  Ilouzeau). 
The  reaction  is  such  that  one-half  of  the  ammonia  is  oxid- 
ized to  nitric  acid,  which  unites  with  the  residue  and  with 
water,  as  illustrated  by  the  equation : 

2  1^11^     +     4  0     =     NH^,  N63     +     H,0 

In  this  manner,  nitrate  of  ammonia  may  originate  in  the 
atmosphere,  since,  as  already  shown,  ammonia  and  ozone 
are  both  present  there. 

Oxidation  and  Reduction  in  the  Atmospliere.  —  The 

fact  that  ammonia  and  organic  matters  on  the  one  hand, 
and  ozone,  nitrous  and  nitric  acids  on  the  other,  are  pres- 
ent, and,  perhaps,  constantly  present  in  the  air,  involves  at 
first  thought  a  contradiction,  for  these  two  classes  of  sub- 
stances are  in  a  sense  incompatible  with  each  other. 
Organic  matters,  ammonia,  and  nitrous  acid,  are  converted 
by  ozone  into  nitric  acid.  On  the  contrary,  certain  or- 
ganic matters  reduce  ozone  to  ordinary  oxygen,  or  destroy 
it  altogether,  and  reduce  nitric  and  nitrous  acids  to  am- 
monia, or,  j)erhaps,  to  free  nitrogen.  The  truth  is  that 
the  substances  named  are  being  perpetually  composed  and 
decomposed  in  the  atmosphere,  and  at  the  surface  of  the 


86  HOW   CROPS   FEED. 

soil.  Here,  or  at  one  moment,  oxidation  j^revails ;  there, 
or  at  another  moment,  reduction  preponderates.  It  is 
only  as  one  or  another  of  the  results  of  this  incessant  ac- 
tion is  withdrawn  from  the  sphere  of  change,  that  we  can 
give  it  permanence  and  identify  it.  The  quantities  we 
measure  are  but  resultants  of  forces  that  oppose  each  oth- 
er. The  idea  of  rest  or  permanence  is  as  foreign  to  the 
chemistry  of  the  atmosphere  as  to  its  visible  phenomena. 

Nitric  Acid  in  the  Atmosphere. — The  occurrence  of  ni- 
tric acid  or  nitrate  of  ammonia  in  the  atmosphere  has  been 
abundantly  demonstrated  in  late  years  (1854-6)  by  Cloez, 
Boussingault,  De  Luca,  and  Kletzinsky,  who  found  that 
when  large  volumes  of  air  are  made  to  bubble  through 
solutions  of  potash,  or  to  stream  over  fragments  of  brick 
or  pumice  which  have  been  soaked  in  potash  or  carbonate 
of  potash,  these  absorbents  gradually  acquire  a  small 
amount  of  nitric  acid.  In  the  experiments  of  Cloez  and 
De  Luca,  the  air  was  first  washed  of  its  ammonia  by  con- 
tact with  sulphuric  acid.  Their  results  prove,  therefore, 
that  the  nitric  acid  was  formed  independently  of  ammonia, 
though  it  doubtless  exists  in  the  air  in  combination  with 
this  base. 

Proportioa  of  Nitric  Acid  ia  llaisi- water,  etc, — In  at- 
mospheric waters,  nitric  acid  is  found  much  more  abund- 
antly than  in  the  air  itself,  for  the  reason  that  a  small  bulk 
of  rain,  etc.,  washes  an  immense  volume  of  air. 

Many  observers,  among  the  first,  Liebig,  have  found  ni- 
trates in  rain-water,  especially  in  the  rain  of  thunder- 
storms. The  investigations  of  Boussingault,  made  in 
1856-8,  have  amply  confirmed  Barral's  observation  that 
nitric  acid  (in  combination)  is  almost  invariably  present  in 
rain,  dew,  fog,  hail,  and  snow.  Boussingault,  {Agro7iomAe^ 
etc.,  II,  325)  determined  the  quantity  of  nitric  acid  in  134 
rains,  31  snows,  8  dews,  and  7  fogs.  In  only  16  instances 
out  of  these  180  was  the  amount  of  nitric  acid  too  small 


ATMOSPHERIC    AIK    AS    THE    FOOD    OF    PLANTS.  87 

to  detect.  The  greatest  proportion  of  nitric  acid  found  in 
rain  occurred  in  a  slow-falling  morning  shower,  (9th  Octo- 
ber, 1857,  at  Liebfrauenberg),  viz.,  62  parts  *  in  10  million 
of  water.  In  fog,  on  one  occasion,  (at  Paris,  19th  Dec, 
1857,)  101  parts  to  10  million  of  water  were  observed. 

Knop  found  in  rain-water,  collected  near  Leipzig,  in 
July,  1862,  56  parts ;  in  rain  that  fell  during  a  thunder- 
storm, 98  parts  in  10  million  of  water. 

Boussingault  found  in  rain  an  average  of  2  parts,  in 
snow  of  4  parts,  of  nitric  acid  to  10  million  of  w^ater. 

Mr.  Way,  whose  determinations  of  ammonia  in  the  at- 
mospheric waters  collected  by  Lawes  and  Gilbert,  at 
Rothamstead,  during  the  whole  of  the  years  1855-6,  have 
already  been  noticed,  (p.  63,)  likewise  estimated  the  nitric 
acid  in  the  same  waters.  He  found  the  proportion  of  ni- 
tric acid  to  be,  in  1855,  4  parts,  in  1856  4J  parts,  to  10 
million  of  water. 

Bretschneider  found  at  Ida-Marienhiitte,  Prussia,  for  the 
year  1865-6  an  average  of  84-  parts,  for  1866-7  an  average 
of  4|-  parts,  of  nitric  acid  in  10  million  of  water.  At  Regen- 
walde,  Prussia,  the  average  in  1865-6  was  25  parts,  in 
1866-7,  22  parts.  At  Proskau,  the  average  in  1864-5  was 
31  parts.  At  Kuschen,  the  average  for  1864-5  was  6 
parts;  in  1865-6,  7;  in  1866-7,  8  parts.  At  Dahme,  in 
1865-6,  the  average  was  12  parts.  At  lusterburg,  Pincus 
'and  RoUig  obtained  in  1864-5,  an  average  of  12  parts;  in 
1865-6,  an  average  of  16  parts  of  nitric  acid  in  10  million 
of  water.  The  highest  monthly  average  was  280  parts, 
at  Lauersfort,  July,  1864;  and  the  lowest  was  nothing, 
April,  1865,  at  Ida-Marienhiitte. 

Quantity  ©f  Nitric  Acid  in  Atmosplieric  Water.— The 
total  quantity  of  nitric  acid  that  could  be  collected  in  the 
rains,  etc.,  at  Rothamstead,  amounted  in  1855  to  2.98  lbs., 
and  in  1856  to  2.80  lbs.  per  acre. 

*  In  all  tbe  quantitative  statements  here  and  elsewhere,  anhydrous  nitric  acid. 
No  O5,  (0=16,  formerly  NO5,  0=8)  is  to  be  uuderstood. 


88 


HOW    CEOPS    FEED. 


This  quantity  was  very  irregularly  distributed  among  the 
months.  In  1855  the  smallest  amount  was  collected  in 
January,  the  largest  in  October,  the  latter  being  nearly 
20  times  as  much  as  the  former.  In  1856  the  largest 
quantity  occurred  in  May,  and  the  smallest  in  February, 
the  former  not  quite  six  times  as  much  as  the  latter. 

The  following  table  gives  the  results  of  Mr.  Way  entire. 
{Jour.  Boy.  Ag.  Soc.  of  Eng.,  XYII,  pp.  144  and  €20.) 

Amoukts  op  Rain  and  of  Ammonia,  Nitric  Acid,  and  total  Nitrogen 
therein,  collected  at  Rothamstead,  Eng.,  in  the  j'ears  1S55-6 — calculated  per 
acre,  according  to  Messrs.  Lawes,  Gilbert,  and  Way. 


January 

February  . . . 

March 

April 

May , 

June 

Jnly 

August 

September.*. 

October 

November . . 
December. . . 

Total. . . . 


(Quantity  of  Eaiti 
in  Imperial  Gal- 
lons, (1  gal.  =  10 
lbs.  water.) 


1855 


13.523 
22.473 
52.484 
9.281 
52.575 
41.295 

157.713 
59.622 
34.875 

124.466 
59.950 
39.075 


1856 


Ammonia 

in 

grains. 


1855    1856 


1244 
2337 
4513 
1141 
4206 


62.952 

30.586 
22.722 
59.083 
106.474 
43.25315574 
33.561  9620 
59.859  4769 
47.477:3313 
65.033  7592 
32.181  3021 
50.870  2438 


5005 
4175 
2108 
8614 
18313 
4870 
2869 
4214 
5972 
3921 
2591 
4070 


Nitric 
acid  in 
grains. 


1855:1856 


230  1561 

9441  544 
1102    806 

325  1063 
184013024 
3303  2046 
2680  1191 
3577  2125 

732' 1756 
448012075 
100711371 

664  2035 


Total  m- 

trogen   in 

grains. 


1855  1856 


1084 
2169 
3995 
1024 
3939 
5447 
8615 
4870 
2917 
7414 
2749 
2180 


4526 
3579 
1945 
7369 
15863 
4540 
2670 
4021 
5373 
3767 
2489- 


663.332    616.051  7.11 
galPs.      gall's,    lbs. 


9.53 

lbs. 


2.98  2.80  6.63    8.31 
lbs.  libs.  libs.    lbs. 


According  to  Pincus  and  Rollig,  the  atmospheric  water 
brought  down  at  Insterburg,  in  the  year  ending  with 
March,  1865,  7.225  lbs.  av.  of  nitric  acid  per  English  acre 
of  surface. 

The  quantity  of  nitrogen  tliat  fell  as  ammonia  was 
3.628  lbs.;  that  collected  in  the  form  of  nitric  acid  was 
1.876  lbs.  The  total  nitrogen  of  the  atmospheric  waters 
per  acre,  for  the  year,  was  5.5  lbs.  The  rain-fall  was 
392.707  imperial  gallons. 

Bretschneider  found  in  the  atmospheric  waters  gathered 
at  Ida-Marienhtitte,  in  Silesia,  during  12  months  ending 
April  15th,  1866,  3f  lbs.  of  nitric  acid  per  acre  of  surface. 

In  Bretsclmeider's  investigation,  the  amount  of  nitrogen 


ATMOSPHERIC    AIR    AS    THE    FOOD    OF    PLAT^TS.  89 

brought  down  per  acre  in  the  form  of  ammonia  was  9.936 
lbs.;  that  in  the  form  of  nitric  acid  was  0.974  lbs.  The 
total  nitrogen  contained  in  the  rain,  etc.,  was  accordingly 
10.91,  or,  in  round  numbers,  11  lbs.  avoirdupois.  The  rain- 
fall amounted  to  488.309  imperial  gallons,  (Wilda's  Cen- 
tralUatt,  August,  1866.) 

Relation  of  Nitric  Acid  to  Ammonia  in  the  Atmos- 
phere.— The  foregoing  results  demonstrate  that  there  is 
in  the  aggregate  an  excess  of  ammonia  over  the  amount 
required  to  form  nitrate  with  the  nitric  acid.  (In  nitrate 
of  ammonia  (NH^  ^^s)?  the  acid  and  base  contain  the 
sanae  quantity  of  nitrogen.)  We  are  hence  justified  in 
assuming  that  the  acid  in  question  commonly  occurs  as  ni- 
trate of  ammonia  *  in  the  atmosphere. 

At  times,  however,  the  nitric  acid  may  preponderate. 
One  instance  is  on  record  [Journal  de  Pharmacie^  Apr., 
1845)  of  the  presence  of  free  nitric  acid  in  hail,  w^hich  fell 
at  Nismes,  in  June,  1842.  This  hail  is  said  to  have  been 
perceptibly  sour  to  the  taste. 

Cloez  {Compt.  Jiendus,  Hi,  527)  found  traces  of  free 
nitric  acid  in  air  taken  3  feet  above  the  ground,  especially 
at  the  beginning  and  end  of  winter. 

The  same  must  have  been  true  in  the  cases  already  giv- 
en, in  which  exceptionally  large  quantities  of  nitric  acid 
^vere  found,  in  the  examinations  made  by  Boussingault  and 
the  Prussian  chemists. 

The  nitrate  of  ammonia  which  exists  in  the  atmosphere 
is  doubtless  held  there  in  a  state  of  mechanical  suspension. 
It  is  dissolved  in  the  falling  rains,  and  when  once  brought 
to  the  surface  of  the  soil,  cannot  again  find  its  way  into 
the  air  by  volatilization,  as  carbonate  of  ammonia  does, 
but  is  permanently  removed  from  the  atmosphere,  and 


*  In  evaporating  large  quantities  of  rain-water  to  dryness,  there  are  often  found 
in  the  residue  nitrates  of  lime  and  soda.  In  these  cases  the  lime  and  soda  come 
from  dust  suspended  in  the  air. 


90  HOW    CROPS    FEED. 

until  in  some  way  chemically  decomposed,  belongs  to  the 
soil  or  to  the  rivers  and  seas. 

Nitrous  Acid  in  the  Atmospheric  Waters. — In  most  of  the  researches  up- 
on the  quantity  of  nitric  acid  in  the  atmosphere  and  meteoric  waters, 
nitrojis  acid  has  not  been  specially  regarded.  The  tests  which  serve  to 
detect  nitric  acid  nearly  all  apply  equally  well  to  nitrous  acid,  and  no 
discrimination  has  "been  made  until  recently.  According  to  Schonbein 
and  Bohlig,  nitrates  are  sometimes  absent  from  rain-water,  but  nitrites 
never.  They  occur,  however,  in  but  minute  proportion.  Pincus  and 
Eollig  observed  but  traces  of  nitrous  acid  in  the  waters  gathered  at 
lusterburg.  Reichardt  found  no  weighable  quantity  of  nitrous  acid  in 
a  sample  of  hail,  the  water  from  which  contained  in  10  million  parts,  33 
parts  ammonia  and  5)^  parts  of  nitric  acid.  It  is  evident,  then,  that 
nitrous  acid,  if  produced  to  any  extent  in  the  atmosphere,  does  not  re- 
main as  such,  but  is  chiefly  oxidized  to  nitric  acid. 

In  any  case  our  data  are  probably  not  incorrect  in  respect  to  the 
quantity  of  Jiitrogen  existing  in  both  the  forms  of  nitrous  and  nitric 
acids,  although  the  former  compound  has  not  been  separately  estimated. 
The  methods  employed  for  the  estimation  of  nitric  acid  would,  in  gen- 
eral, include  the  nitrous  acid,  with  the  single  error  of  bringing  the  latter 
into  the  reckoning  as  a  part  of  the  former. 

Nitric  Acid  as  Food  of  Plants,— A  multitude  of  obser- 
vations, both  in  the  field  and  laboratory,  demonstrate  that 
nitrates  greatly  promote  vegetable  growth.  The  extensive 
use  of  nitrate  of  soda  as  a  fertilizer,  and  the  extraordinary 
fertility  of  the  tropical  regions  of  India,  whose  soil  until 
lately  furnished  a  large  share  of  the  nitrate  of  potash  of 
commerce,  attest  the  fact.  Furthermore,  in  many  cases, 
nitrates  have  been  found  abundantly  in  fertile  soils  of  tem- 
perate climates. 

Experiments  in  artificial  soil  and  in  water-culture  show 
not  only  that  nitrates  supply  nitrogen  to  plants,  but  dem- 
onstrate beyond  doubt  that  the'y  alone  are  a  sufficient 
source  of  this  element,  and  that  no  other  compound  is  so 
well  adapted  as  nitric  acid  to  furnish  crops  with  nitrogen. 

Like  ammonia-salts,  the  nitrates  intensify  the  color,  and 
increase,  both  absolutely  and  relatively,  the  quantity  of 
nitrogen  of  the  plant  to  which  they  are  supplied.  Their 
efiect,  when  in  excess,  is  also  to  favor  the  development  of 
foliage  at  the  expense  of  fruit. 


ATMOSPHERIC    AIK    AS    THE    FOOD    OF    PLANTS.  91 

The  nitrates  do  not  appear  to  be  absorbed  by  the  plant 
to  any  great  extent,  except  through  the  medium  of  the 
soil,  since  they  cannot  exist  in  the  state  of  vapor  and  are 
brought  down  to  the  earth's  surface  by  atmospheric  waters. 

The  full  discussion  of  their  nutritive  eifects  must  there- 
fore be  deferred  until  the  soil  comes  under  notice.  See 
Division  II,  p.  271. 

In  §  10,  p.  96,  "Recapitulation  of  the  Atmospheric^^ 
Supplies  of  Food  to  Crops,"  the  inadequacy  of  the  at- 
mospheric nitrates  will  be  noticed. 


9. 


OTHER  INGREDIENTS  OF  THE  ATMOSPHERE;    viz.,  3farsh  Gas, 

Carbonic   Oxide,  j^itrous  Oxide,  Hydrochloric  Acid,  Sulphurous  Acid, 

Sulphydric  Acid,  Organic  Vapors,  Suspe?ided  Solid  Matters. 

There  are  several  other  gaseous  bodies,  some  or  all  of  •which  may  oc- 
cur in  the  atmosphere  in  very  minute  quantities,  but  whose  relations  to 
vegetation,  in  the  present  state  of  our  knowledge,  appear  to  be  of  no 
practical  moment.  Since,  however,  they  have  been  the  subjects  of  in- 
vestigations or  disquisition  by  agricultural  chemists,  they  require  to  be 
briefly  noticed. 

Wlarsli  CJas,"^  C  H4. — This  substance  is  a  colorless  and  nearly 
odorless  gas,  which  is  formed  almost  invariably  when  organic  matters 
suffer  decomposition  in  absence  of  oxygen.  When  a  lump  of  coal  or  a 
billet  of  wood  is  strongly  heated,  portions  of  carbon  and  hydrogen 
unite  to  form  this  among  several  other  substances.  It  is  accordingly 
one  of  the  ingredients  of  the  gases  whose  combustion  forms  the  flame 
of  all  fires  and  lamps.  It  is  also  produced  in  the  decay  of  vegetable  mat- 
ters, especially  when  they  are  immersed  in  Avater,  as  happens  in  swamps 
and  stagnant  ponds,  and  it  often  bubbles  in  large  quantities  from  the 
bottom  of  ditches,  when  the  mud  is  stirred. 

Pettenlvofer  and  Volt  have  lately  found  that  marsh  gas  is  one  of  the 
gaseous  products  of  the  respiration  or  nutrition  of  animals.    - 

It  is  combustible  at  high  temperatures,  and  burns  with  a  yellowish, 
faintly  luminous  flame,  to  water  and  carbonic  acid.  It  causes  no  ill  ef- 
fects when  breathed  by  animals  if  it  be  mixed  with  much  air,  though  of 
itself  it  cannot  support  respiration. 


*  Known  also  to  chemists  under  the  names  of  Light  Carburetted  Hydrogen, 
Hydride  of  Methyl  and  Methane. 


92  HO^    CHOPS    FEED. 

The  mode  or  ifs  origin  at  once  suggests  its  presence  in  the  atmos- 
phere. Saussure  observed  that  commou  air  contains  some  suseous  com- 
pound or  compounds  of  carbon,  besides  carbonic  acid;  and  Boussin- 
gault  found  in  ISSI  tbal  the  air  at  Paris  contained  a  ye ry  small  quantity 
(from  tvo  to  eight-miUionths)  of  hydrogen  in  some  form  of  combina- 
tion besides  ^ater.  These  facts  agree  with  the  supposition  that  marsh 
gas  is  a  normal  though  minute  and  variable  ingredient  of  the  atmosphere. 

fSelatlosLs  of  Marsli  €ras  to  Teg^etation.— Whether 
tliis  gas  is  absorbed  and  assimilated  by  plants  is  a  point  on  which  we 
have  at  present  no  information.  It  might  serve  as  a  source  both  of  car- 
bon and  hydrogen ;  but  as  these  bodies  are  amply  furnished  by  carbonic 
acid  and  water,  and  as  it  is  by  no  means  improbable  that  marsh  iras  it- 
self is  actually  converted  into  these  substances  by  ozone,  the  question 
CI  its  assimilatiou  is  one  of  little  importance,  and  remains  to  be  inves- 
tigated. 

Schultz  (Johnston's  Lectures  o?i  Ag.  Chejju,  2d  Ed.,  147)  found  on  sev- 
eral occasions  that  the  gas  evolved  from  plants  when  exposed  to  the  sun- 
light, instead  of  being  pure  oxygen,  contained  a  combustible  admixture, 
s  ;>  that  it  exploded  violently  on  contact  with  a  lighted  taper. 

This  observation  shows  either  that  the  healthy  plants  evolved  a  large 
amount  of  marsh  gas,  which  forms  with  oxygen  an  esrplosive  mixture 
(the  fire-damp  of  coal-mines),  or,  as  is  most  probable,  that  the  vegetable 
matter  entered  into  decomposition  from  too  long  continuance  of  the 
experiment. 

Boussingault  has,  however,  recently  found  a  minute  proportion  of 
marsh  gas  in  the  air  exhaled  from  the  leaves  of  plants  that  are  exposed 
to  sunlight  ich£Ti  submerged  in  icaier.  It  does  not  appear  when  the  leaves 
are  surrounded  by  air,  as  the  latest  experiments  of  Boussingatilt,  Cloez, 
and  CoreiLwi-der.  agree  in  demonstrating. 

Cai'lioiiic  Oxide,  CO.  is  a  gas  destitute  of  color  and  odor.  It 
bums  in  contact  with  air,  with  a  flame  that  has  a  fine  blue  color.  The 
result  of  its  combustion  is  carbonic  acid,  CO  -r  O  =  CO;. 

This  gas  is  extremely  poisonous  to  animals.  Air  containing  a  few 
per  cent  of  it  is  unfit  for  respiration,  and  produces  headache,  insensi- 
bility, and  death. 

Carbonic  oxide  may  be  obtained  artificially  by  a  variety  of  processes. 
If  carbonic  acid  gas  be  made  to  stream  slowly  through  a  tube  containing 
ignited  charcoal,  it  is  converted  into  carbonic  oxide,  CO2  -f  C  =  2  CO. 

Carbonic  oxide  is  largely  produced  in  all  ordinary  fires.  The  air  which 
craws  through  a  grate  heaped  with  well-ignited  coals,  as  it  enters  the 
bottom  of  the  mass  of  fuel,  loses  a  large  portion  of  its  oxygen,  which 
there  unites  with  carbon,  fonning  carbonic  acid.  This  gas  is  carried  up 
into  the  heated  coal,  and  there,  where  carbon  is  in  excess,  it  takes  up  an- 
other proportion  of  this  element-,  being  converted  into  carbonic  oxide. 
At  the  smnmit  of  the  fire,  where  oxygen  is  abnndant,  the  carbonic  oxide 
bums  again  with  its  peculiar  blue  color,  to  carbonic  acid,  provided  the 
heat  be  intense  enough  to  inflame  the  gas,  as  is  the  case  when  the  mass 


ATMOSPHERIC   AIE    AS   THE    FOOD    OF   PLANTS.  93 

of  fuel  is  thorouglily  ignited.  When,  on  tlie  other  liand,  the  fire  is  cov- 
ered with  cold  fuel,  carbonic  oxide  escapes  copiously  into  the  atmos- 
phere. 

When  crystallized  oxalic  acid  is  heated  wjtli  oil  of  vitriol,  it  yields 
■water  to  the  latter,  and  falls  into  a  mixture  of  carhouic  acid  and  carbonic 
oxide. 

C2H2O4,   2H2O     =    CO2'    +     CO     +     3H2O. 

Carbonic  oxide  may,  perhaps,  be  formed  in  small  quantity  in  the  de- 
cay of  organic  matters;  though  Corenwinder  {Compt.  Iie7id.,  LX,  102) 
failed  to  detect  it  in  the  rotting  of  manure. 

ISelations  of  Carl>OBsic  Oxid.e  to  Tcgetatiom. — Ac- 
cording to  Saussure,  while  pea-plants  languish  and  die  when  immersed 
in  carbonic  oxide,  certain  marsh  plants  {Epilobium  Idrsutum^  Lythrum 
salicaria,  and  Polygonum  persicaria)  flourish  as  well  in  this  gas  as  in  com- 
mon air.  Saussure's  experiments  with  these  plants  lasted  six  weeks. 
There  occurred  an  absorption  of  the  gas  and  an  evolution  of  oxygen. 
It  is  thus  to  be  inferred  that  carbonic  oxide  may  be  a  source  of  carbon 
to  aquatic  plants. 

Boussingault  {Compt  Rencl.^  LXI,  493)  was  unable  to  detect  any  action 
of  the  foliage  of  land  plants  upon  carbonic  oxide,  cither  when  the  gas 
■was  pure  or  mixed  with  air. 

The  carbonic  oxide  which  Boussingault  found  in  1863  in  air  exhaled 
from  submerged  leaves,  proves  to  have  been  produced  in  the  analyses, 
(from  pyrogallate  of  potash,)  and  was  not  emitted  by  the  leaves  them- 
selves, as  at  first  supposed,  as  both  Cloez  and  Boussingault  have  shown. 

]\'itroiis  Oxide,  N2O.— This  substance,  the  so-called  laughing 
gas,  is  prepared  from  nitrate  of  ammonia  by  exposing  that  salt  to  a  heat 
somewhat  higher  than  is  necessary  to  fuse  it.  The  salt  decomposes  into 
nitrous  oxide  and  water. 

NH4,  NO3  =  N2O   +  2  H2O. 

The  gas  is  readily  soluble  in  water,  and  has  a  sweetish  odor  and  taste. 
When  breathed,  it  at  first  produces  a  peculiar  exhilarating  efiect,  which 
is  followed  by  stupor  and  insensibility. 

This  gas  has  never  been  demonstrated  to  exist  in  the  atmosphere.  In 
fact,  our  methods  of  analysis  are  incompetent  to  detect  it,  when  it  is 
present  in  very  minute  quantity  in  a  gaseous  mixture.  Knop  is  of  the 
opinion  that  nitrous  oxide  may  occur  in  the  atmosphere,  and  has  pub- 
lished an  account  of  experiments  {Journal  fur  Prakt.  Chem.^  Vol.  59, 
p.  Hi)  which,  according  to  him,  prove  that  it  is  absorbed  by  vegetation. 

Until  nitrous  oxide  is  shown  to  be  accessible  to  plants,  any  further  no- 
tice of  it  is  unnecessary  in  a  treatise  of  this  kind. 

Ilydrocltlorlc  Acid,  ^as,  HCl,  whose  properties  have  been 
described  in  How  Crops  Grow,  p.  118,  is  found  in  minute  quantity  in  the 
air  over  salt  marshes.  It  doubtless  proceeds  from  the  decomposition  of 
the  chloride  of  magnesium  of  sea-water.    Sprengel  has  surmised  its  ex- 


94  HOY/    CEOPS    FEED. 

halation  by  sea-shore  plants.  It  is  found  in  the  air  near  soda-worlis,  be- 
ing a  product  of  the  manufacture,  and  is  destructive  to  vegetation. 

SwlpliMi*OHS  Acid,  SO2,  and  Ssilpliyclric  Acid,  HS,  (sec 
H.  C.  G.,  p.  115,)  may  exist  in  the  atmosphere  as  local  emanations.  In 
large  quantities,  as  when  escaping  from  smelting  works,  roasting  heaps, 
or  manufactories,  they  often  prove  destructive  to  vegetation.  In  contact 
with  air  they  quickly  suffer  oxidation  to  sulphuric  acid,  which,  dissolv- 
ing in  the  water  of  rains,  etc.,  becomes  incorporated  with  the  soil. 

Orgaiaic  Matters  of  whatever  sort  that  escape  as  vapor  into  the 
atmosphere  and  are  there  recognized  by  their  odor,  are  rapidly  oxidized 
and  have  no  direct  influence  upon  vegetation,  so  far  as  is  now  known. 

^sBspcBided  ^olid  Matters  in  t"3ae  Atanosplaerc. — 
The  solid  matters  which  are  raised  into  the  air  by  winds  in  the  form  of 
dust,  and  are  often  transported  to  great  heights  and  distances,  do  not 
properly  belong  to  the  atmosphere,  but  to  the  soil.  Their  presence  in 
the  air  exr[3lains  the  growth  of  certain  plants  {air-plants)  when  entirely 
disconnected  from  the  soil,  or  of  such  as  are  found  in  pure  sand  or  on 
the  surface  of  rocks,  incapable  of  performing  the  functions  of  the  soil, 
except  as  dust  accumulates  upon  them. 

Barral  announced  in  1862  {Jour.  d'Ag.  pratique y/p.  150)  the  discovery 
of  phosphoric  acid  in  rain-water.  Robinet  and  Luca  obtained  the  same 
result  with  water  gathered  near  the  surface  of  the  earth.  The  latter 
found,  however,  that  rain,  collected  at  a  height  of  60  or  more  feet  above 
the  ground,  was  free  from  it. 

g   10. 

RECAPITULATION    OF    THE   ATMOSPHERIC    SUPPLIES    OF 
FOOD  TO  CROPS. 

Oxygen,  whether  required  in  the  free  state  to  effect 
chemical  changes  in  the  processes  of  organization,  or  in 
combination  (in  carbonic  acid)  to  become  an  ingredient 
of  the  plant,  is  superabundantly  supplied  by  the  atmos- 
phere. 

Carl>011, — The  carbonic  acid  of  the  atmosphere  is  a 
source  of  this  element  sufficient  for  the  most  rapid  growth, 
as  is  abundantly  demonstrated  by  the  experiments  in  wa- 
ter culture,  made  by  Nobbe  and  Siegert,  and  by  Wolff, 
(H.  C.  G.,  p.  170),  in  which  oat  and  buckv\rheat  plants 
were  brought  to  more  than  the  best  agricultural  develop- 


AT.MOSPHEEIC    AIE    AS    THE    POOD    OF    PLANTS. 


95 


ment,   witli    no    other   than  the    atmospheric    supply   of 
carbon. 

Hydrogen  is  adequately  supplied  to  trops  by  water, 
which  equally  belongs  to  the  Atmospher^nd  the  Soil, 
although  it  enters  the  plant  chiefly  from  the  latter^ 

Nitrogen  exists  in  immense  quantities  in  the  atmosphere, 
and  we  may  regard  the  latter  as  the  primal  source  of  this 
element  to  the  organic  world.  In  the  atmosphere,  how- 
ever, nitrogen  exists  for  the  most  part  in  the  free  state,  and 
is,  as  such,  so  we  must  believe  from  existing  evidence,  un- 
assimilable  by  crops.  Its  assimilable  compounds,  ammo- 
nia and  oiitrio  acid^  occur  in  the  atmosphere,  but  in  pro- 
portions so  minute,  as  to  have  no  influence  on  vegetable 
growth  directly  appreciable  by  the  methods  of  investiga- 
tion hitherto  employed,  unless  they  are  collected  and  con- 
centrated by  rain  and  dew. 

The  subjoined  Table  gives  a  summary  of  the  amount 

of  nitrogen  annually  brought  down  in  rain,  snow,  etc., 

upon  an  acre  of  surface,  according  to  the  determinations 

hitherto  made  in  England  and  Prussia. 

Amount   of   Assimilable   Nitrogen   annually   bkought   down   by 
THE  Atmospheric  Waters. 


Locality. 


Year. 


Nitrogen 
per  Ac7'e. 


Water 
per  Acre. 


Rotliaxnstead,  Southern  England 

Kuschen,  Province  Posen,  Prussia 

Insterburg,  near  Konigsberg,  " 

Regenwalde,  near  Stettin,  " 

Ida-Mar i en hijtte,  near  Breslau,  Silesia,  " 
Proskau,  Silesia,  " 

Dahme,  Province  Brandenburg,  " 


1855* 

1856* 

18&4-5+ 

1865-61- 

1864-5+ 

1865-6+ 

1864-5+ 

1865-6+ 

1865* 

1864-5$ 

1865* 


6.63 

8.31 

1.86 

2.50 

5.49 

6.81 

15.09 

10.38 

11.83 

20.91 

6.66 


lbs, 


6,633,220  lbs. 

6,160.510  " 

2,680,086  " 

4,008,491  " 

6,222,461  " 

5.383,478  " 

5,313,562  " 

4,358,053  " 

4,877,545  " 

4,031,782  " 

3,868,646  " 


Average. 


8.76  lbs.  4.867.075Ibs. 


*  From  Jan.  to  Jan.    +  From  Apr.  to  Apr.    %  From  May  to  May. 

Direct  Atmospheric  Supply  of  Nitrogen  Insufficient 

for  CropSe — To  estimate  the  adequacy  of  these  atmos- 
pheric supplies  of  assimilable  nitrogen,  we  may  compare 
their  amount  with  the  quantity  of  nitrogen  required  in  the 


96  now  CKOPS  feed. 

composition  of  standard  crops,  and  with  the  quantity  con- 
tained in  appropriate  applications  of  nitrogenous  fertil- 
izers. 

The  average  atmospheric  supply  of  nutritive  nitrogen 
in  rain,  etc.,  for  12  months,  as  above  given,  is  much  less 
than  is  necessary  for  ordinary  crops.  According  to  Dr. 
Anderson,  the  nitrogen  in  a  crop  of  28  bushels  of  wheat 
and  1  (long)  ton  3  cwt.  of  straw,  is  45^  lbs.;  that  in  2| 
tons  of  meadow  hay  is  56  lbs.  The  nitrogen  in  a  crop  of 
clover  hay  of  2^  (long)  tons  is  no  less  than  108  lbs.  Ob- 
viously, therefore,  the  atmospheric  waters  alone  are  in- 
capable of  furnishing  crops  with  the  quantity  of  nitrogen 
they  require. 

On  the  other  hand,  the  atmospheric  supply  of  nitrogen 
by  rain,  etc.,  is  not  inconsiderable,  compared  with  the 
amount  of  nitrogen,  which  often  forms  an  effective  manur- 
ing. Peruvian  guano  and  nitrate  of  soda  (Chili  saltpeter) 
each  contain  about  15  per  cent  of  nitrogen.  The  nitrogen 
of  rain,  estimated  by  the  average  above  given,  viz.,  8f  lbs., 
corresponds  to  58  lbs.  of  these  fertilizers.  200  lbs.  of  gua- 
no is  for  most  field  purposes  a  sufficient  application,  and 
400  lbs.  is  a  large  manuring.  In  Great  Britain,  where  ni- 
trate of  soda  is  largely  employed  as  a  fertilizer,  112  lbs. 
of  this  substance  is  an  ordinary  dressing,  which  has  been 
known  to  double  the  grass  crop. 

We  notice,  however,  that  the  amount  of  nitrogen  sup 
plied  in  the  atmospheric  waters  is  quite  variable,  as  well 
for  different  localities  as  for  different  years,  and  for  differ- 
ent periods  of  the  year.  At  Kuschen,  but  2-2|-  lbs.  Avere 
brought  down  against  21  lbs.  at  Proskau.  At  Regenwalde 
the  quantity  was  15  lbs.  in  1864-5,  but  the  next  year  it 
was  nearly  30  per  cent  less.  In  1855,  at  Rothamstead, 
the  greatest  rain  supply  of  nitrogen  was  in  July,  amount- 
ing to  1^  lbs.,  and  in  October  nearly  as  much  more  was 
brought  down;  the  least  fell  in  January.  In  1856  the 
largest  amount,  2^  lbs.,  fell  in  May;  the  next,  1  lb.,  in 


ATMOSPHEIUC    AIR    AS    THE    FOOD    OF    PLANTS.  97 

April;  and  the  least  in  March.  At  Ida-Marienhiitte, 
Kuschen,  and  Regenwalde,  in  1865-6,  nearly  half  the 
year's  atmospheric  nitrogen  came  down  in  summer ;  but 
at  Insterburg  only  30  per  cent  fell  in  summer,  while  40 
'^er  cent  came  down  in  winter. 

The  nitrogen  that  is  brought  down  in  winter,  or  in 
espring  and  autumn,  when  the  fields  are  fallow,  can  be 
counted  upon  as  of  use  to  summer  crops  only  so  far  as  it 
remains  in  the  soil  in  an  assimilable  form.  It  is  well 
known  that,  in  general,  much  more  water  evaporates  from 
cultivated  fields  during  the  summer  than  falls  upon  them 
in  the  same  period  ;  while  in  winter,  the  water  that  falls 
is  in  excess  of  that  which  evaporates.  But  how  mucli  of 
the  winter's  fall  comes  to  supply  the  summer's  evaporation, 
is  an  element  of  the  calculation  likely  to  be  very  variable, 
and  not  as  yet  determined  in  any  instance. 

We  conclude,  then,  that  the  direct  atmospheric  supply 
of  assimilable  nitrogen,  though  not  unimportant,  is  insuf- 
ficient for  crops. 

We  must,  therefore,  look  to  the  soil  to  supply  a  large 
share  of  this  element,  ns  well  as  to  be  the  medium  through 
which  the  assimilable  atmospheric  nitrogen  chiefly  enters 
the  plant. 

The  Other  Ingredients  of  the  Atmosphere,  so  far  as 
we  now  know,  are  of  no  direct  significance  in  the  nutri- 
tion of  agricultural  plants.  Indirectly,  atmospheric  ozone 
has  an  influence  on  the  supplies  of  nitric  acid,  a  point  we 
shall  recur  to  in  a  full  discussion  of  the  question  of  the 
Supplies  of  Nitrogen  to  Vegetation,  in  a  subsequent 
chapter. 

§    11- 

ASSIMILATION  OF  ATMOSPHERIC  FOOD. 

Boussingault  has  suggested  the  very  probable  view  that 

the  first  process  of  assimilation  in  the  chlorophyll  cells  of 

the  leaf, — where,  under  the  solar  influence,  carbonic  acid 

5 


98  HOW    CEOPS    FEED. 

is  absorbed  and  decomposed,  and  a  nearly  equal  volume 
of  oxygen  is  set  free, — consists  in  the  simultaneous  deox- 
idation  of  carbonic  acid  and  of  water,  whereby  the  former 
is  reduced  to  carbonic  oxide  with  loss  of  half  its  oxygen, 
and  the  latter  to  hydrogen  with  loss  of  all  its  oxygen,  viz.: 

Carbonic  Wafp        =  ^<^^^<^^^^'^  -j_  ^]/<^^o-  Oxy- 

acid  °  oxide       '      (/en.  gen. 

CO,  +  H,0  =  CO  +  H,  +  O, 
In  this  reaction  the  oxygen  set  free  is  identical  in  bulk 
with  the  carbonic  acid  involved,  and  the  residue  retained 
in  the  plant,  COH^,  multiplied  by  12,  would  give  12 
molecules  of  carbonic  oxide  and  24  atoms  of  hydrogen, 
which,  chemically  united,  might  constitute  either  glucose 
or  levulose,  C^^  ^i\  ^i2>  from  which  by  elimination  of 
H^O  would  result  cane  sugar  and  Arabic  acid,  while  sepa- 
ration of  2H2O  would  give  cellulose  and  the  other  mem- 
bers of  its  group. 

Whether  the  real  chemical  process  be  this  or  a  different 
and  more  complicated  one  is  at  present  a  matter  of  vague 
probabihty.  It  is,  notwithstanding,  evident  that  this  re- 
action expresses  one  of  the  principal  results  of  the  assim- 
ilation of  Carbon  and  Hydrogen  in  the  foliage  of  plants. 

§    12. 

The  following  Tabular  View  may  usefully  serve  the 

reader  as  a  recapitulation  of  the  chapter  now  finished. 

TABULAR  VIEW  OF  THE  EELATIONS  OF  THE  ATMOSPHERIC 
INGREDIENTS  TO  THE  LIFE  OF  PLANTS. 

'Oxygen,  by  roots,  flowers,  ripening  fruit,   and  by  all 

growing  parts. 
Carbonic  Acid,  by  foliage  and  green  parts,  but  only  in 
the  light. 

Absorbed    J  Ammonia,  as  carbo7iate,  by  foliage,  probably  at  all  times. 
by  Plants.     I  Water,  as  liquid,  through  the  roots. 

Nitrous  Acid  )  united  to  ammonia,  and  dissolved  in  wa- 
NiTRic  Acid    )        ter  through  the  roots. 

Ozone  [uncertain, 

Marsh  Gas  ) 


THE  ATMOSPHERE  AS  BELATED  TO  VEGETATION.   99 

Not  absorbed  j  Nitrogen. 
by  Plants.     I  Water  in  state  of  yapor. 

'  Oxygen,  [  by  foliage  and  green  parts,  but  only  in  the 

Exhaled  by      O^^^^^"    '         ^'S^^' 

Plants         '  Marsh  Gas  in  traces  by  aquatic  plants  ? 

Water,  as  vapor,  from  surface  of  plant  at  all  times. 
Carbonic  Acid,  from  the  growing  parts  at  all  timesT 


CHAPTER     II. 

THE    ATMOSPHERE    AS    PHYSICALLY    BELATED    TO 
VEGETATION. 

§  1' 
MANNER  OF  ABSORPTION  OF  GASEOUS  FOOD  BY  THE  PLANT. 

Closing  here  our  study  of  the  atmosphere  considered  as 
a  source  of  the  food  of  j^lants,  we  still  need  to  remark 
somewhat  upon  the  physical  properties  of  gases  in  rela- 
tion to  vegetable  life ;  so  far,  at  least,  as  may  give  some 
idea  of  the  means  by  which  they  gain  access  into  the 
plant. 

Physical  Constitution  of  the  Atmosphere.— That  the 

atmosphere  is  a  mixture  and  not  a  chemical  combination 
of  its  elements  is  a  fact  so  evident  as  scarcely  to  require 
discussion.  As  we  have  seen,  the  proportions  which  sub- 
sist among  its  ingredients  are  not  uniform,  although  they 
are  ordinarily  maintained  within  very  narrow  limits  of  va- 
riation. This  is  a  sufficient  proof  that  it  is  a  mixture. 
The  remarkable  fact  that  very  nearly  the  same  relative 
quantities  of  Oxygen,  Nitrogen,  and  Carbonic  Acid, 
steadily  exist  in  the  atmosphere  is  due  to  the  even  balance 
which  obtains  between  growth  and  decay,  between  life 
and  death.     The  equally  remarkable  fact  that  the  gases 


100  HOW    CEOPS   PEED. 

Avhicli  compose  the  atmosphere  are  uniformly  mixed  to- 
gether without  regard  to  their  specific  gravity,  is  but  one 
result  of  a  law  of  nature  which  we  shall  immediately 
notice. 

Diffusion  of  leases , — Whenever  two  or  more  gases  are 
brought  into  contact  in  a  confined  space,  they  instantly 
begin  to  intermingle,  and  continue  so  to  do  until,  in  a 
longer  or  shorter  time,  they  are  both  equally  diffused 
throughout  the  room  they  occupy.  If  two  bottles,  one 
filled  with  carbonic  acid,  the  other  with  hydrogen,  be  con- 
nected by  a  tube  no  wider  than  a  straw,  and  be  j)laced  so 
that  the  heavy  carbonic  acid  is  below  the  fifteen  times 
lighter  hydrogen,  we  shall  find,  after  the  lapse  of  a  few 
hours,  that  the  two  gases  have  mingled  somewhat,  and  in 
a  few  days  they  will  be  in  a  state  of  uniform  mixture.  On 
closer  study  of  this  phenomenon  it  has  been  discovered 
that  gases  diffuse  with  a  rapidity  proportioned  to  their 
lightness,  the  relative  diffusibility  being  nearly  in  the  in- 
verse ratio  of  the  square  roots  of  their  specific  gravities. 
By  interposing  a  porous  diaphragm  between  two  gases  of 
different  densities,  we  may  visibly  exhibit  the  fact  of  their 
ready  and  unequal  diffusion.  For  this  purpose  the  dia- 
phragm must  offer  a  partial  resistance  to  the  movement 
of  the  gases.  Since  the  lighter  gas  passes  more  rapidly 
into  the  denser  than  the  reverse,  the  space  on  one  side  of 
the  membrane  will  be  overfilled,  while  that  on  the  other 
side  will  be  partially  emptied  of  gas. 

In  the  accompanying  figure  is  represented  a  long  glass 
tube,  5,  widened  above  into  a  funnel,  and  having  cemented 
upon  this  an  inverted  cylindrical  cup  of  unglazed  jDorce- 
lain,  a.  The  funnel  rests  in  a  round  aperture  made  in  the 
horizontal  arm  of  the  support,  while  the  tube  below  dips 
beneath  the  surface  of  some  water  contained  in  the  wine- 
glass. Tlie  jDorous  cup,  funnel,  and  tube,  being  occupied 
with  common  air,  a  glass  bell,  c,  is  filled  with  hydrogen 
gas  and  placed  over  the  cup,  as  shown  in  the  figure.     In- 


THE    ATMOSPHERE    AS    EELATED    TO    VEGETATIOX.      101 


stantly,  bubbles  begin  to  escape  rapidly  from  the  bottom 
of  the  tube  through  the  water  of  the  wine-glass,  thus 
demonstrating  that  hydrogen  passes  into  the  cup  faster 
than  air  can  escape  outwards 
through  its  pores.  If  the  bell  be 
removed,  the  cup  is  at  once  bathed 
again  externally  in  common  air,  the 
light  hydrogen  floating  instantly 
upwards,  and  now  the  water  begins 
to  rise  in  the  tube  in  consequence  of 
the  return  to  the  outer  atmosphere 
of  the  hydrogen  which  before  had 
diffused  into  the  cup. 

It  is  tbe  perpetual  action  of  this 
diffusive  tendency  which  maintains 
the  atmosphere  in  a  state  of  such 
uniform  mixture  that  accurate  ana- 
lyses of  it  give  for  oxygen  and 
nitrogen  almost  identical  figures,  at 
all  times  of  the  day,  at  all  seasons, 
all  altitudes,  and  all  situations,  ex- 
cept near  the  central  surface  of 
large  bodies  of  still  water.  Here, 
the  fact  that  oxygen  is  more  largely 
absorbed  by  water  than  nitrogen, 
diminishes  by  a  minute  amount  the 
usual  proportion  of  the  former  gas. 
If  in  a  limited  volume  of  a  mixture  of  several  gases  a 
solid  or  liquid  body  be  placed,  which  is  capable  of  chemic- 
ally uniting  with,  or  otherwise  destroying  the  aeriform 
condition  of  one  of  the  gases,  it  will  at  once  absorb  those 
particles  of  this  gas  which  lie  in  its  immediate  vicinity, 
and  thus  disturb  the  uniformity  of  the  remaining  mixture. 
Uniformity  at  once  tends  to  be  restored  by  diffusion  of  a 
portion  of  the  un absorbed  gas  into  the  space  that  has  been 
deprived  of  it,  and  thus  the  absorption  and  the  diffusion 


Fig.  7. 


102  HOW    CROPS   FEED. 

keep  pace  with  each  other  until  all  the  absorbable  air  is 
removed  from  the  gaseous  mixture,  and  condensed  or  fixed 
in  the  absorbent. 

In  this  manner,  a  portion  of  the  atmosphere  enclosed  in 
a  large  glass  vessel  may  be  perfectly  freed  from  watery 
vapor  and  carbonic  acid  by  a  small  fragment  of  caustic 
potash.  By  standing  over  sulphuric  acid,  ammonia  is 
taken  from  it ;  a  piece  of  phosphorus  will  in  a  few  hours 
absorb  all  its  oxygen,  and  an  ignited  mass  of  the  rare 
metal  titanium  will  remove  its  nitrogen. 

Osmose  of  Gases. — By  this  expression  is  understood  the 
passage  of  gaseous  bodies  through  membranes  whose 
poises  are  too  small  to  he  discoverable  by  optical  means^ 
such  as  the  imperforate  wall  of  the  vegetable  cell,  the 
green  cuticle  of  the  plant  where  not  interrupted  by  stomata^ 
vegetable  parchment,  India  rubber,  and  animal  membranes, 
like  bladder  and  similar  visceral  integuments. 

If  a  bottle  filled  with  air  have  a  thin  sheet  of  India 
rubber,  or  a  piece  of  moist  bladder  tied  over  its  mouth 
and  then  be  placed  within  a  bell  of  hydrogen,  evidence  is 
at  once  had  that  gases  penetrate  the  membrane,  for  it 
swells  outwards,  and  may  even  burst  by  the  pressure  of 
the  hydrogen  that  rapidly  accumulates  in  the  bottle. 

Gaseous  Osmose  is  Difiusion  Modified  by  the  Influence 
of  the  Memhrane. — ^The  rapidity  of  osmose  *  is  of  course 
influenced  by  the  thickness  of  the  membrane,  and  the 
character  of  its  pores.  An  adhesion  between  the  mem- 
brane and  the  gases  would  necessarily  increase  their  rate 
of  penetration.  In  case  the  membrane  should  attract  or 
have  adhesion  for  one  gas  and  not  for  another,  complete 
separation  of  the  two  might  be  accomplished,  and  in  pro- 
portion to  the  difierence  existing  between  two  gases  as  re- 
gards adhesion  for  a  given  membrane,  would  be  the  de- 
gree to  which  such  gases  would  be  separated  from  each 


*  The  osmose  of  liquids  is  discussed  in  detail  in  "How  Crops  Grow,"  p.  354. 


THE    ATMOSPHERE    AS    RELATED   TO    VEGETATI01S-.      103 

Other  in  penetrating  it.  In  case  a  membrane  is  moistened 
with  water  or  other  liquid,  or  by  a  solution  of  solid  mat- 
ters, this  would  still  further  modify  the  result. 

Absorption  of  (Jases  by  the  Plant  .—A  few  words  will 
now  suffice  to  apply  these  facts  to  the  absorption  of  the 
nutritive  gases  by  vegetation.  The  foliage  of  plants  is 
freely  permeable  to  gases,  as  has  been  set  forth  in  "  How 
Crops  Grow,"  p.  289.  The  cells,  or  some  portions  of  their 
contents,  absorb  or  condense  carbonic  acid  and  ammonia 
in  a  similar  way,  or  at  least  with  the  same  effect,  as  potash 
absorbs  carbonic  acid.  As  rapidly  as  these  bodies  are 
removed  from  the  atmosphere  surrounding  or  occupying 
the  cells,  they  are  re-supplied  by  diffusion  from  without ; 
so  that  although  the  quantities  of  gaseous  plant-food  con- 
tained in  the  air  are,  relatively  considered,  very  small, 
they  are  by  this  grand  natural  law  made  to  flow  in  con- 
tinuous streams  toward  every  growing  vegetable  celL 


DIVISION  II. 

THE    SOIL   AS    RELATED   TO   VEGETABLE 
PRODUCTION. 

CHAPTER    I. 

I  N  T  R  O  D  U  C  T  O  Pw  T . 

For  the  Husbandman  the  Soil  has  this  paramount  im- 
portance, that  it  is  the  home  of  the  roots  of  his  crops  and 
the  exclusive  theater  of  his  labors  in  j)romoting  their 
growth.  Through  it  alone  can  he  influence  the  amount 
of  vegetable  production,  for  the  atmosphere,  and  the  light 
and  heat  of  the  sun,  are  altogether  beyond  his  control. 
Agriculture  is  the  culture  of  the  field.  The  value  of  the 
field  lies  in  the  quality  of  its  soil.  E'o  study  can  have  a 
grander  material  significance  than  the  one  which  gives  us 
a  knowledge  of  the  causes  of  fertility  and  barrenness,  a 
knowledge  of  the  means  of  economizing  the  one  and  over- 
coming the  other,  a  knowledge  of  those  natural  laws 
which  enable  the  farmer  so  to  modify  and  manage  his  soil 
that  all  the  deficiencies  of  the  atmosphere  or  the  vicissi- 
tudes of  climate  cannot  deprive  him  of  a  suitable  reward 
for  his  exertions. 

The  atmosphere  and  all  extra-terrestrial  influences  that 
afiect  the  growth  of  plants  are  indeed  in  themselves 
beyond  our  control  We  cannot  modify  them  in  kind  or 
amount ;  but  we  can  influence  their  subserviency  to  our 
purposes  through  the  medium  of  the  soil  by  a  proper  un- 
derstanding of  the  characters  of  the  latter. 
104 


Il^TTBODUCTOET.  105 

The  General  Functions  ®f  the  Soil  are  of  three  kinds : 

1.  The  ashes  of  the  plant  whose  nature  and  variations 
have  been  the  subject  of  study  in  a  former  volume  (H. 
C.  G.,  pp.  111-201,)  are  exclusively  derived  from  the  soil. 
The  latter  is  then  concerned  in  the  most  direct  manner 
with  the  nutrition  of  the  plant.  The  substances  which 
the  plant  acquires  from  the  soil,  so  far  as  they  are  nutri- 
tive, may  be  collectively  termed  soil-food. 

2.  The  soil  is  a  mechanical  support  to  vegetation.  The 
roots  of  the  plant  penetrate  the  pores  of  the  soil  in  all 
directions  sidewise  and  downward  from  the  point  of  their 
junction  with  the  stem,  and  thus  the  latter  is  firmly 
braced  to  its  upright  position  if  that  be  natural  to  it,  and 
in  all  cases  is  fixed  to  the  source  of  its  supplies  of  ash-in- 
gredients. 

3.  By  virtue  of  certain  special  (physical)  qualities  to  be 
hereafter  enumerated,  the  soil  otherwise  contributes  to 
the  well-being  of  the  plant,  tempering  and  storing  the 
heat  of  the  sun  which  is  essential  to  the  vital  processes ; 
regulating  the  supplies  of  food,  which,  coming  from  itself 
or  from  external  sources,  form  at  any  one  time  but  a  mi- 
nute fraction  of  its  mass,  and  in  various  modes  ensuring  the 
co-operation  of  the  conditions  which  must  unite  to  produce 
the  perfect  plant. 

Variety  of  Soils. — In  nature  we  observe  a  vast  variety 
of  soils,  which  differ  as  much  in  their  agricultural  value 
as  they  do  in  their  external  appearance.  We  find  large 
tracts  of  country  covered  with  barren,  drifting  sands,  on 
whose  arid  bosom  only  a  few  stunted  pines  or  shriveled 
grasses  find  nourishment.  Again  there  occur  in  the  high- 
lands of  Scotland  and  Bavaria,  as  well  as  in  Prussia,  and 
other  temperate  countries,  enormous  stretches  of  moor- 
land, bearing  a  nearly  useless  growth  of  heath  or  moss. 
In  Southern  Russia  occurs  a  vast  tract,  two  hundred  mil- 
lions of  acres  in  extent,  of  the  tschornosem^  or  black  earth, 


106  now    CROPS    TEED. 

which  is  remarkable  for  its  extraordinary  and  persistent 
fertility.  The  prairies  of  our  own  West,  the  bottom  lands 
of  the  Scioto  and  other  rivers  of  Ohio,  are  other  examples 
of  peculiar  soils ;  while  on  every  farm,  almost,  may  be 
found  numerous  gradations  from  clay  to  sand,  from  vege- 
table mould  to  gravel — gradations  in  color,  consistence, 
comjDOsition,  and  productiveness. 


CHAPTER    II. 

ORIGIN    AND    FORMATION    OF    SOILS. 

Some  consideration  of  the  origin  of  soils  is  adapted  to 
assist  in  understanding  the  reasons  of  their  fertility. 
Geological  studies  give  us  reasons  to  believe  that  what  is 
now  soil  was  once,  in  chief  part,  solid  rock.  We  find  in 
nearly  all  soils  fragments  of  rock,  recognizable  as  such  by 
the  eye,  and  by  help  of  the  microscope  it  is  often  easy  to 
perceive  that  those  portions  of  the  soil  which  are  impal- 
r)able  to  the  feel  are  only  minuter  grains  of  the  same  rock. 

Rocks  are  aggregates  or  mixtures  of  certain  tninerals. 

Minerals,  again,  are  chemical  compounds  of  various  ele^ 
ments. 

We  have  therefore  to  consider : 

I.  The  Chemical  Elements  of  Rocks. 

II.  The  Mineralogical  Elements  of  Rocks. 

III.  The  Rocks  themselves — their  Kinds  and  Special 
Characters. 

ly.  The  Conversion  of  Rocks  into  Soils ;  to  which  we 
may  add : 

Y.  The  Incorporation  of  Organic  Matter  with  Soils. 


ORIGIN   AND    FORMATION    OF    SOILS.  107 

§    1- 
THE  CHEMICAL  ELEMENTS  OF  ROCKS. 

The  chemical  elements  of  rocks,  i.  e.,  the  constituents 
of  the  minerals  which  go  to  form  rocks,  include  all  the 
simple  bodies  known  to  science.  Those,  which,  from  their 
universal  distribution  and  uses  in  agriculture,  concern  us 
immediately,  are  with  one  exception  the  same  that  have 
been  noticed  in  a  former  volume  as  composing  the  ash  of 
agricultural  plants,  viz..  Chlorine,  Sulphur,  Carbon,  Silicon, 
Potassium,  Sodium,  Calcium,  Magnesium,  Iron,  and  Man- 
ganese. The  description  given  of  these  elements  and 
of  their  most  important  compounds  in  "  How  Crops  Grow  " 
will  suffice.  It  is  only  needful  to  notice  further  a  single 
element. 

AlumiRum,  Symbol  Al.,  At.  wt.  27 A,  is  a  bluish  silver- 
white  metal,  characterized  by  its  remarkable  lightness, 
having  about  the  specific  gravity  of  glass.  It  is  now 
manufactured  on  a  somewhat  large  scale  in  Paris  and  New- 
castle, and  is  employed  in  jewelry  and  ornamental  work. 
It  is  prepared  by  a  costly  and  complex  process  invented 
by  Prof.  Deville,  of  Paris,  in  1854,  which  consists  essen- 
tially in  decomposing  chloride  of  aluminum  by  metallic 
sodium,  at  a  high  heat,  chloride  of  sodium  (common 
salt)  and  metallic  aluminum  being  produced,  as  shown  by 
the  equation,  Al,^  CI,  +  6  Na  =  6  N"a  CI  +  2  Al. 

By  combining  with  oxygen,  this  metal  yields  but  one 
oxide,  which,  like  the  highest  oxide  of  iron,  is  a  sesqui- 
oxide,  viz.: 

Alumina,  Al^  O3,  Eq.  102.8.— When  alum  (double  sul- 
phate of  alumina  and  potash)  is  dissolved  in  water  and 
ammonia  added  to  the  solution,  a  white  gelatinous  body 
separates,  which  is  alumina  combined  with  water,  Al^  O3, 
3  H^O.  By  drying  and  strongly  heating  this  hydrated 
alumina,  a  white  powder  remains,  which  is  pure  alumina. 


108  HOW    CROPS    FEED. 

In  nature  alumina  is  found  in  the  form  of  emery.  The 
sapphire  and  ruby  are  finely  colored  crystallized  varieties 
of  alumina,  liigMy  prized  as  gems. 

Hydrated  alumina  dissolves  in  acids,  yielding  a  numer- 
ous class  of  salts,  of  whicli  the  sulphate  and  acetate  are 
largely  employed  in  dyeiog  and  calico-printing.  The  sul- 
phate of  alumina  and  potash  is  familiarly  known  imder 
the  name  of  alum,  with  which  all  are  acquainted.  Other 
compounds  of  alumina  will  be  noticed  presently. 

§2. 

MINERALOGICAL  ELEMENTS  OF  EOCKS. 

The  mineralogical  elements  or  minerals  *  which  compose 
rocks  are  very  numerous. 

But  little  conception  can  be  gained  of  the  appearance 
of  a  mineral  from  a  description  alone.  Actual  inspection 
of  the  different  varieties  is  necessary  to  enable  one  to  rec- 
ognize them.  The  teacher  should  be  provided  with  a 
collection  to  illustrate  this  subject.  The  true  idea  of  their 
composition  and  use  in  forming  rocks  and  soils  may  be 
gathered  quite  well,  however,  from  the  written  page.  For 
minute  information  concerning  them,  see  Dana's  Manual 
of  Mineralogy.     We  shall  notice  the  most  important. 

Quartz. — Chemically  speaking,  this  ixiineral  is  anhy- 
drous silica — silicic  acid — a  compound  of  silicon  and  ox- 
ygen, Si  O^.  It  is  one  of  the  most  abundant  substances 
met  with  on  the  earth's  surface.  It  is  found  in  nature  in 
six-sided  crystals,  and  in  irregular  masses.  It  is  usually 
colorless,  or  white,  irregular  in  fracture,  glassy  in  luster. 
It  is  very  hard,  readily  scratching  glass.  (See  H.  C.  G., 
p.  120.) 

Feldspar  (field-spar)  is,  next  to  quartz,  the  most  abund- 


*  The  word  mineral,  or  mineral  "species,"  here  implies  a  definite  chemical 
compound  of  natural  occurrence. 


OEIGIX   AND    FORMATIO:?^    OF    SOILS.  109 

ant  mineral.  It  is  a  compound  of  silica  with  alumina^ 
and  with  one  or  inore  of  the  alkalies,  and  sometimes  vnth 
lime.  Mineralogists  distinguish  several  species  of  feld- 
spar according  to  their  composition  and  crystallization. 
Feldspar  is  found  in  crystals  or  crystalline  masses  usually 
of  a  white,  yellow,  or  flesh  color,  with  a  somewhat  pearly 
luster  on  the  smooth  and  level  surfaces  which  it  presents 
on  fracture.  It  is  scratched  by,  and  does  not  scratch 
quartz. 

In  the  subjoined  Table  are  given  the  mineralogical  names 
and  analyses  of  the  principal  varieties  of  feldspar.  Ac- 
companying each  analysis  is  its  locality  and  the  name  of 
the  analyst. 


Orthoclase. 

Albite. 

Oligoclase, 

Labradorite. 

Comrmn  or -poUhsTi 

Sodafeldspar. 

Soda-lime  feldspar 

Lime-soda 

feldspar. 

feldspar. 

NewRochelle,N.Y. 

Unionville,  Pa. 

Haddam,  Conn, 

Drummond,  C.  W. 

S.  W.  Johnson. 

M.  C.  Weld. 

G.  J.  Brush. 

T.  S.  Hunt. 

Silica,                 64.23 

66.86 

64.26 

54.70 

Alumina,             20.42 

21.89 

21.90 

29.80 

Potash,                12.47 

0.50 

0.33 

Soda,                     2.62 

8. 78 

9.99 

2.44 

Lime,                  trace 

1.79 

2.15 

11.42 

Ma<?nesia,           

0.48 



Oxide  of  iron,    trace 

0.36 

m^er,                  0.24 

0.48 

0.29 

0.40 

M'ica  is,  perhaps,  next  to  feldspar,  the  most  abundant 
mineral.  There  are  three  principal  varieties,  viz.:  Musco- 
vite, Phlogopite,  and  Biotite.  They  are  silicates  of  alumi- 
na with  potash,  magnesia,  lime,  iron,  and  manganese. 

Mica  bears  the  common  name  "  isinglass."  It  readily 
splits  into  thin,  elastic  plates  or  leaves,  has  a  brilliant 
luster,  and  a  great  variety  of  colors, — white,  yellow,  brown, 
green,  and  black.  Muscovite,  or  muscovy  glass,  is  some- 
times found  in  transparent  sheets  of  great  size,  and  is  used 
in  stove-doors  and  lamp-chimneys.  It  contains  much 
alumina,  and  potash,  or  soda,  and  the  black  varieties  oxide 
of  iron. 

Phlogopite  and  Biotite  contain  a  large  percentage  of 
magnesia,  and  often  of  oxide  of  iron. 


110  HOW    CEOPS    FEED. 

The  following  analyses  represent  these  varieties. 

Muscovite.  Phlogopite.  Biotite. 


Litchfield,  Mt.Leinster,  Edwards,  N.  Burgess,  Putnam  Co., 

Conn.  Ireland.  N.  Y.  Canada.  N.  Y.  Siberia. 
Smith  &  Brash.  Haughton.  W.J. Craw.  T.S.Huut.  Smith  &  Brush.  H.  Ros6. 

Silica,             44.60  44.64  40.36  40.97  39.62  40.00 

Alumina,        36.23  30.18  16.45  18.56  17.35  12.67 

Oxide  of  iron,  1.34  6.35  trace  5.40  19.03 

<^^i^eof          0  g3 

manganese, 

Magnesia,       0.37  0.72  29.55  25.80  23.85  15.70 

Lime,               0.50               

Potash,             6.20  12.40  7.23  8.26  8.95  5.61 

Soda,                4.10               4.94  1.08  1.01                

Water,             5.26  5.32  0.95  1.00  1.41                

Yarlable  Composition  of  Minerals. — We  notice  in  the 
micas  that  two  analyses  of  the  same  species  differ  very 
considerably  in  the  proportion,  and  to  some  extent  in  the 
kind,  of  their  ingredients.  Of  the  two  muscovites  the 
first  contains  6°|g  more  of  alumina  than  the  second,  while 
the  second  contains  S^j^  more  of  oxide  of  iron  than  the 
first.  Again,  the  second  contains  12.4"  1^  of  potash,  but  no 
soda  and  no  lime,  while  the  first  reveals  on  analysis  4"|  ^  of 
soda  and  0.5°  1^,  of  lime,  and  contains  correspondingly  less 
potash.  Similar  differences  are  remarked  in  the  other  anal- 
yses, especially  in  those  of  Biotite. 

In  fact,  of  the  analyses  of  more  than  50  micas  which  are 
given  in  mineralogical  treatises,  scarcely  any  two  per- 
fectly agree.  The  same  is  true  of  many  other  minerals, 
especially  of  the  amphiboles  and  pyroxenes  presently  to  be 
noticed.  In  accordance  with  this  variation  in  composition 
we  notice  extraordinary  diversities  in  the  color  and  ap- 
pearance of  different  specimens  of  the  same  mineral. 

This  fact  may  appear  to  stand  in  contradiction  to  the 
statement  above  made  that  these  minerals  are  definite 
combinations.  In  the  infancy  of  mineralogy  great  per- 
plexity arose  from  the  numerous  varieties  of  minerals  that 
were  found — varieties  that  agreed  together  in  certain  char- 
acteristics, but  widely  differed  in  others. 


OEIGnq-    AND    FOEMATION    OF    SOILS.  Ill 

IsOMOrpblSM. — In  1830,  Mitscherlich,  a  Prussian  phi- 
losopher, discovered  that  a  number  of  the  elementary 
bodies  are  capable  oi  replacing  each  other  in  combination^ 
from  the  fact  of  their  natural  crystalline  form  being  identic- 
al ;  they  being,  as  he  termed  it,  is  amorphous^  or  of  like 
shape.  Thus,  magnesia,  lime,  protoxide  of  iron,  protoxide 
of  manganese,  which  are  all  protoxide-hases^  form  one 
group,  each  of  whose  members  may  take  the  place  of  the 
other.  Alumina  (Al^  O^)  and  oxide  of  iron  (Fe^  O3)  be- 
long to  another  group  of  sesquioxide-hases,  one  of  which 
may  replace  the  other;  while  in  certain  combinations 
silica  and  alumina  replace  each  other  as  acids. 

These  replacements,  which  may  take  place  indefinitely 
within  certain  limits,  thus  may  greatly  affect  the  composi- 
tion without  altering  the  constitution  of  a  mineral.  Of 
the  mineral  amphihole,  for  example,  there  are  known  a 
great  number  of  varieties ;  some  pure  white  in  color,  con- 
taining, in  addition  to  silica,  magnesia  and  lime ;  others 
pale  green,  a  small  portion  of  magnesia  being  replaced  by 
protoxide  of  iron;  others  black,  containing  alumina  in 
place  of  a  portion  of  silica,  and  with  oxides  of  iron  and 
manganese  in  large  proportion.  All  these  varieties  of 
amphibole,  however,  admit  of  one  expression  of  their 
constitution,  for  the  amount  of  oxygen  in  the  bases,  no 
matter  what  they  are,  or  what  their  proportions,  bears  a 
constant  relation  to  the  oxygen  of  the  silica  (and  alumina) 
they  contain,  the  ratio  being  1:2. 

If  the  protoxides  be  grouped  together  under  the  gen- 
eral symbol  MO  (metallic  protoxide,)  the  composition  of 
the  amphiboles  may  be  expressed  by  the  formula  MO  SiO^. 

In  pyroxene  the  same  replacements  of  protoxide-bases 
on  the  one  hand,  and  of  silica  and  alumina  on  the  other, 
occur  in  extreme  range.  (See  analyses,  p.  112.)  The  gen- 
eral formula  which  includes  all  the  varieties  of  pyroxene 
is  the  same  as  that  of  amphibole.  The  distinction  of  am- 
phibole from  pyroxene  is  one  of  crystallization. 


112 


HOW    CROPS   FEED. 


We  miglit  give  in  the  same  style  formulsB  for  all  the 
minerals  noticed  in  these  pages,  but  for  our  purposes  this 
is  unnecessary. 

Amphibole  is  an  abundant  mineral  often  met  with  in 
distinct  crystals  or  crystalline  and  fibrous  masses,  varying 
in  color  from  pure  white  or  gray  {tremolite,  asbestns),  light 
green  (cictinoUte),  grayish  or  brownish  green  {anthophyl- 
Ute),  to  dark  green  and  black  {horntlende)  ^  according  as 
it  contains  more  or  less  oxides  of  iron  and  manganese. 
It  is  a  silicate  of  magnesia  and  lime,  or  of  magnesia  and 
protoxide  of  iron,  with  more  or  less  alkalies. 


V^hite. 

Gray. 

Ash-gray. 

Black. 

Leek- green. 

Gouverneur, 

Lanark, 

Cummington, 

Brevig, 

Waldheim, 

N.  Y. 

Canada. 

Mass. 

Norway. 

Saxony. 

Rammelsberg, 

T.  S.  Hunt. 

Smith  &  Brush. 

Plantamour. 

Knop. 

Silica, 

57.40 

55.30 

50.74 

46.57 

58.71 

Magnesia, 

24.69 

22.50 

10.31 

5.88 

10.01 

Lime, 

13.89 

13.38 

trace 

5.91 

11.53 

Protoxide  of 

iron. 

1.36 

6.30 

33.14 

24.38 

5.65 

Protoxide  of 

trace 

1.77 

2.07 

manganese, 

Alumina, 

1.38 

0.40 

0.89 

3.41 

1.52 

Soda, 

0.80 

0.54 

7.79 

12.38 

Potash, 

0.25 

trace 

2.96 

Water, 

0.40 

0.30 

3.04 

0.50 

Pyroxene  is  of  very  common  occurrence,  and  consider- 
ably resembles  hornblende  in  colors  and  in  composition. 


White. 

Gray-  White. 

Green. 

Black. 

Black. 

Ottawa, 

Bathurst, 

Lake 

Orange  Co., 

Wetterau, 

Canada. 

Canada. 

Champlain, 

N.  Y. 

T.  S.  Hunt, 

.  T.  S.  Hunt. 

Seybert. 

Smith  &  Brush. 

Gmelin. 

Silica, 

54.50 

51.50 

50.38 

39.30 

56.80 

Magnesia, 

18.14 

17.69 

6.83 

2.98 

5.05 

Lime, 

25.87 

23.80 

19.3:3 

10.39 

4.85 

Protoxide 
of  iron, 

1.98 

20.40 

30.40 

12.06 

Sesquioxide 
of  iron. 

0.35 

Protoxide  of 
manganese, 

trace 

0.67 

3.72 

Alumina, 

6.15 

1.83 

9.78 

15.32 

Soda, 

1.66 

3.14 

Potash, 

2.48 

0.34 

Water, 

0.40 

1.10 

1.95 

ORIGIN    AND    FORMATION    OF    SOILS.  113 

Chlorite  is  a  common  mineral  occurring  in  small  scales 
or  plates  which,  are  brittle.  It  is  soft,  usually  exists  in 
masses,  rarely  crystallized^  and  is  very  variable  in  color 
and  composition,  though  in  general  it  has  a  grayish  or 
brownish-green  color,  and  contains  magnesia,  alumina,  and 
iron,  united  with  silica.     See  analysis  below. 

Lewcite  is  an  anhydrous  silicate  of  alumina  found 
chiefly  in  volcanic  rocks.  It  exists  in  white,  hard,  24-sid- 
ed crystals.  It  is  interesting  as  being  formed  at  a  high 
heat  in  melted  lava,  and  as  being  the  first  mineral  in  which 
j)otash  was  discovered  (by  Klaproth,  in  1797).  See  anal- 
ysis below. 

Knolmite  is  a  hydrous  silicate  of  alumina,  w^hich  is 
l^roduced  by  the  slow  decomposition  of  feldspar  under  the 
action  of  air  and  water  at  the  usual  temperature.  Form- 
ed in  this  way,  in  a  more  or  less  impure  state,  it  consti- 
tutes the  mass  of  white  porcelain  clay  or  kaolin,  which  is 
largely  used  in  making  the  finer  kinds  of  pottery.  It  ap- 
pears in  white  or  yellowish  crystalline  scales  of  a  pearly 
luster,  or  as  an  amorphous  translucent  powder  of  extreme 
fineness.     Ordinary  clay  is  a  still  more  impure  kaolinite. 


Chlorite, 

Steele  Mine,  N. 

Leucite, 
C.    Vesuvius, 

Kaolinite. 

Summit  Hill, 

Chaudiere 

Eruption  of  1857 

Pa«         : 

Falls,  Canada. 

Genth. 

Eammelsberg. 

S.  W.  Johnson. 

,  T.S.Hunt. 

Silica, 

SI. 90 

57.24 

45.93 

46.05 

Alumina, 

21.77 

22.96 

39.81 

38.37 

Sesquioxide  of  iron,              4.60 

Protoxide  of  iron, 

ai.si 

Protoxide  of  manganese,     1.15 



Magnesia, 

12.78 



0.63 

Lime, 

0.91 

0.61 

Soda, 

0.93 

Potash, 

18.61 

Water, 

10.59 

14.02 

14.00 

Talc  is  often  found  in  pale-green,  flexible,  inelastic  scales 
or  leaves,  but  much  more  commonly  in  compact  gray 
masses,  and  is  then  known  as  soapstone.     It  is  very  soft. 


114  HOW    CEOPS    FEED. 

has  a  greasy  feel,  and  in  composition  is  a  hydrous  silicate 
of  magnesia.     See  analysis. 

Serpentine  is  a  tough  but  soft  massive  mineral,  in  color 
usually  of  some  shade  of  green.  It  forms  immense  beds 
in  E'ew  England,  N'ew  York,  Pennsylvania,  etc.  It  is  also 
a  hydrous  silicate  of  magnesia.     See  analysis. 

Chrysolite  is  a  silicate  of  magnesia  and  iron,  which 
is  found  abundantly  in  lavas  and  basaltic  rocks.  It  is  a 
hard,  glassy  mineral,  usually  of  an  olive  or  brown-green 
color.     See  analysis  below. 


Talc. 

Serpentine. 

Chrysolite. 

Bristol,  Conn. 

New  Haven,  Conn. 

Bolton,  Mass, 

Dr.  Lummis. 

G.  J.  Brush. 

G.  J.  Brush. 

Silica, 

64.00 

4i.05 

40.94 

Alumina, 

0.27 

Protoxide  of  iron. 

4.75 

2.53 

4.37 

Magnesia, 

27.47 

39.24 

50.84 

Lime, 

1.20 

Water, 

4.30 

13.49 

3.28 

Zeolites. — Under  this  general  name  mineralogists  are 
in  the  habit  of  including  a  nimiber  of  minerals  which  have 
recently  acquired  considerable  agricultural  interest,  since 
they  represent  certain  compounds  which  we  have  strong 
reasons  to  believe  are  formed  in  and  greatly  influence  the 
properties  of  soils.  They  are  hydrous  silicates  of  alum- 
ina or  lime,  and  alkali,  and  are  remarkable  for  the  ease 
with  which  they  undergo  decomposition  under  the  influ- 
ence of  weak  acids.  We  give  here  the  names  and  compo- 
sition of  the  most  common  zeolites.  Their  special  signif- 
icance will  come  under  notice  hereafter.  We  may  add 
that  while  they  all  occur  in  white  or  red  crystallizations, 
often  of  great  beauty,  they  likewise  exist  in  a  state  of 
division  so  minute  that  the  eye  cannot  recognize  them, 
and  thus  form  a  large  share  of  certain  rocks,  which,  by 
their  disintegration,  give  origin  to  very  fertile  soils 


ORIGIN"   AND    FORMATION    OF    SOILS.  115 

Ajstalcime.  Chabasite.  Nateolite.  Scolecite.  Thomsonite. 

Lake  Superior.  Nova  Scotia.  Bergen  Hill,  Ghaut's  Tun-       Magnet 

N.  J.  nel,  India.  Cove,  Ark. 

C.  T.  Jackson.  Rammelsberg.     Brush.  P.  Collier.  Smith  &  Brush. 

Silica,                53.40  52.14              47.31  45.80  36.85 

Alumina,          22.40  19.14               26.77  25.55  29.42 

Potash,               0.98                0.35  0.30  

Soda,                   8.52  0.71               15.44  0.17  3.91 

Lime,                   3.00  7.&4                0.41  13.97  13.95 

Magnesia,           

Sesquioxide       __                 ^_g5 

of  iron,  "                ' 

Water,                 9.70  19.19                9. 84  14.28  13.80 

Stilbite.      Apophyllite.    Pectolite.  Laumontite.  Leonhabdite. 

Nova  Scotia.  Lake  Superior.  Bergen  Hill.  Phippshurgh,  Me.  Lake  Sup'r. 

S.W.  Johnson.  J.  L.  Smith.  J.  D.  Whitney.  Dufrenoy.  Barnes. 

Silica,          57.63                 52.08                 55.66  51.98  55.04 

Alumina,     16.17                   1.45  21.12  22.34 

Potash,          4.93                   

Soda,              1.55                   8.89  

Lime,              8.08                  25.30                  32.86  11.71  10.64 

Water,         16.07                 15.92                   2.96  15.05  11.93 

Calcite,  or  Carbonate  of  Lime^  CaO  CO^,  exists  in  na- 
ture in  immense  quantities  as  a  mineral  and  rock.  Mar- 
ble, chalk,  coral,  limestone  in  numberless  varieties,  consist 
of  this  substance  in  a  greater  or  less  state  of  purity. 

Magnesite,  or  CarlonaU  of  Ilagnesia,  MgO  CO^,  oc- 
curs to  a  limited  extent  as  a  white  massive  or  crystallized 
mineral,  resembling  carbonate  of  lime. 

Dolomite,  CaO  CO^  +  MgO  CO,,  is  a  compound  of  car- 
bonate of  lime  with  carbonate  of  magnesia  in  variable 
proportions.  It  is  found  as  a  crystallized  mineral,  and  is 
a  very  common  rock,  many  so-called  marbles  and  lime- 
stones consisting  of  or  containing  this  mineral. 

Cfjpsum,  orHydrous  Sulphate  of  Lime^  CaO  SO3  +  H^O, 
is  a  mineral  that  is  widely  distributed  and  quite  abundant 
in  nature.  "When  "boiled"  to  expel  the  water  it  is 
Plaster  of  Paris. 

Pyrites,  or  Bisulphide  of  Iron,  Fe  S^,  a  yellow  shining 
mineral  often  found  in  cubic  or  octahedral  crystals,  and 
frequently  mistaken  for  gold  (hence  called  fool's  gold), 


116 


HOW    CROPS    FEED. 


is  of  almost  universal  occurrence  in  small  quantities.  Some 
forms  of  it  easily  oxidize  when  exposed  to  air,  and  furnish 
the  green-vitriol  (sulphate  of  protoxide  of  iron)  of  com- 
merce. 

Apatite  and  Phosphorite  e — These  names  are  applied  to 
the  native  i^hosphate  of  lime,  which  is  usually  combined 
with  some  chlorine  and  fluorine,  and  may  besides  contain 
other  ingredients.  Apatite  exists  in  considerable  quantity 
at  Hammond  and  Gouverneur,  in  St.  Lawrence  Co.,  ]^. 
Y.,  in  beautiful,  transparent,  green  crystals ;  at  South 
Burgess,  Canada,  in  green  crystals  and  crystalline  masses ; 
at  Hurdstown,  IN".  J.,  in  yellow  crystalline  masses;  at 
Krageroe,  Xorway,  in  opaque  flesh-colored  crystals.  In 
minute  quantity  apatite  is  of  nearly  universal  distribution. 
The  following  analyses  exhibit  the  composition  of  the 
principal  varieties. 

Krageroe,  Hurdstown, 

Norway.  N'ew  Jersey. 

Yoelcker.  J.  D.  Whitney. 

53.84  53.37 

41.25  42.23 

4.10  1.02 

1.23  ?  ? 

0.29  trace 

0.38 

0.17 

0.42 


Lime, 

Phosphoric  acid, 
Chlorine, 
Fluorine,"^ 
Oxide  of  iron, 
Alumina, 
Potash  and  soda, 
Water, 


Phosphorite  is  the  usual  designation  of  the  non-crystal- 
Ime  varieties. 

Apatite  may  be  regarded  as  a  mixture  in  indefinite 
proportions  of  two  isomorphous  compounds,  chlorapatite 
and  Jlicorapatite,  neither  of  which  has  yet  been  found  pure 
in  nature,  though  they  have  been  produced  artificially. 


*  Fluorine  was  not  determined  in  these  analyses.    The  figures  given  for  this 
element  are  calculated  (by  Rammelsberg),  and  are  probably  not  far  from  the  truth. 


OEIGI2^   AND    rOKMATION    OF    SOILS.  117 

These  substances  are  again  compounds  of  phosphate  of 
lime,  3  CaO  ^fi^-,  with  chloride  of  calcium,  Ca  Cl^,  or 
fluoride  of  calcium,  Ca  Fl^,  respectively. 

§  3. 
EOCKS— THEIK  KINDS  AND  CHARACTERS. 

The  Rocks  which  form  the  solid  (unbroken)  mass  of 
the  earth  are  sometimes  formed  from  a  single  mineral,  but 
usually  contain  several  minerals  in  a  state  of  more  or  less 
intimate  mixture. 

We  shall  briefly  notice  those  rocks  which  have  the 
greatest  agricultural  importance,  on  account  of  their  com- 
mon and  wide-spread  occurrence,  and  shall  regard  them 
principally  from  the  point  of  view  of  their  chemical  com^ 
position^  since  this  is  chiefly  the  clue  to  their  agricultural 
significance.  Some  consideration  of  the  origin  of  rocks, 
as  well  as  of  their  structure^  will  also  be  of  service. 

Igneous  Rocks. — A  share  of  the  rocks  accessible  to 
our  observation  are  plainly  of  igneous  origin^  i.  e.,  their 
existing  form  is  the  one  they  assumed  on  cooling  down 
from  a  state  of  fusion  by  heat.  Such  are  the  lavas  that 
flow  from  volcanic  craters. 

Sedimentary  Rocks. — Another  share  of  the  rocks  are 
oi  aqueous  origin,  i.  e.,  their  materials  have  been  deposit- 
ed from  water  in  the  form  of  mud,  sand,  or  gravel,  the 
loose  sediment  having  been  afterwards  cemented  and  con- 
solidated to  rock.  The  rocks  of  aqueous  origin  are  also 
termed  sedimentary  rocJcs. 

Metamorphic  Rocks. — Still  another  share  of  the  rocks 
have  resulted  from  the  alteration  of  aqueous  sediments  or 
sedimentary  rocks  by  the  efiect  of  heat.  Without  sufier- 
ing  fusion,  the  original  materials  have  been  more  or  less 
converted  into  new  combinations  or  new  forms.  Thus 
limestone  has  been  converted  into  statuary  marble,  and 


118  now    CROPS    FEED. 

clay  into  granite.  These  rocks,  which  are  the  result  of 
the  united  action  of  heat  and  water,  are  termed  meta- 
morphic  (i.  e.,  metamorphosed)  rocks. 

One  of  the  most  obvious  division  of  rocks  is  into  Crys- 
talline  and  Fragmental. 

Crystalline  Rocks  are  those  whose  constituents  crystal- 
lized at  the  time  the  rock  was  formed.  Here  belong  both 
the  igneous  and  metamorphic  rocks.  These  are  often 
plainly  crystalline  to  the  eye,  i.  e.,  are  composed  of  readily 
perceptible  crystals  or  crystalline  grains,  like  statuary 
marble  or  granite ;  but  they  are  also  frequently  made  up 
of  crystals  so  minute,  that  the  latter  are  only  to  be  recog- 
nized by  tracing  them  into  their  coarser  varieties  (basalt 
and  trap.) 

Fragmental  Rocks  are  the  sedimentary  rocks,  formed 
by  the  cementing  of  the  fragments  of  other  older  rocks 
existing  as  mud,  sand,  etc. 

The  Ceystalline  Rocks  may  be  divided  into  two 
great  classes,  viz.,  the  silicious  and  calcareous  y  the  first 
class  containing  silica,  the  latter,  lime,  as  the  predomina- 
ting ingredient. 

The  silicious  rocks  fall  into  three  parallel  series,  which 
have  close  relations  to  each  other.  1.  The  Granitic  series  ; 
2.  The  Syenitic  series;  3.  The  Talcose  or  Magnesian 
series.  In  all  the  siUcious  rocks  quartz  or  feldspar  is  a 
prominent  ingredient,  and  in  most  cases  these  two  minerals 
are  associated  together.  To  the  above  are  added,  in  the 
granitic  series,  mica  ;  in  the  syenitic  series,  amphihole  or 
pyroxene  /  and  in  the  talcose  series,  talc,  chlorite,  or  ser- 
pentine. The  proportions  of  these  minerals  vary  indef- 
initely. 

The  Granitic  Series 
coiisisting  principally  of  Quartz,  Feldspar,  and  Mica. 

Granite,  —  A  hard,   massive*   rock,    either   finely   or 


*  Rocks  arc  massive  when  they  have  no  tendency  to  split  iuto  slabs  or  plates. 


OEIGIN    AND    FOKMATIOlSr    OF    SOILS.  119 

coarsely  crystalline,  of  various  shades  of  color,  depending 
on  the  color  and  proportion  of  the  constituent  minerals, 
usually  gray,  grayish  white,  or  flesh-red.  In  common 
granite  the  feldspar  is  orthoclase  (potash-feldspar).  A 
variety  contains  albite  (soda-feldspar).  Other  kinds  (less 
common)  contain  oligoclase  and  lahradorite. 

Gneiss  differs  from  granite  in  containing  more  mica,  and 
in  having  a  banded  appearance  and  schistose  "^  structure, 
due  to  the  distribution  of  the  mica  in  more  or  less  parallel 
layers.  It  is  cleavable  along  the  planes  of  mica  into 
coarse  slabs. 

Mica-slate  or  Mica-schist  contains  a  still  larger  pro- 
portion of  mica  than  gneiss ;  it  is  perfectly  schistose  in 
structure,  splitting  easily  into  thin  slabs,  has  a  glistening 
appearance,  and,  in  general,  a  grayish  color.  The  coarse 
whetstones  used  for  sharpening  scythes,  which  are  quar- 
ried in  Connecticut  and  Rhode  Island,  consist  of  this  min- 
eral. 

Argillite,  Clay-slate,  is  a  rock  of  fine  texture,  often 
not  visibly  crystalline,  of  dull  or  but  slightly  glistening 
surface,  and  having  a  great  variety  of  colors,  in  general 
black,  but  not  rarely  red,  green,  or  light  gray.  Argillite 
has  usually  a  slaty  cleavage,  i.  e.,  it  splits  into  thin  and 
smooth  plates.  It  is  extensively  quarried  in  various  local- 
ities for  roofing,  and  writing-slates.  Some  of  the  finest 
varieties  are  used  for  whetstones  or  hones. 

Other  Granitic  Rocks. — Sometimes  ^^cc^  is  absent ;  in 
other  cases  the  rock  consists  nearly  or  entirely  of  feldspar 
alone,  or  of  quartz  alone,  or  of  mica  and  quartz.  The 
rocks  of  this  series  often  insensibly  gradate  into  each  oth- 
er, and  by  admixture  of  other  minerals  run  into  number- 
less varieties. 


*  Schists  or  schistose  rocks  are  those  which  have  a  tendency  to  break  into 
slabs  or  plates  from  the  arrangement  of  some  of  the  mineral  ingredients  in 
layers. 


120  how  crops  feed. 

The    Stenitic   Series 
consisting  chiefly  of  Quartz,  Feldspar,  and  AmpJiihole. 

Syenite  is  granite,  save  that  amphibole  takes  the  place 
of  mica.  In  appearance  it  is  like  granite;  its  color  is  usu- 
ally dark  gray.  Syenite  is  a  very  tough  and  durable  rock, 
often  most  valuable  for  building  purposes.  The  famous 
Quincy  granite  of  Massachusetts  is  a  syenite.  Syenitic 
Gtieiss  and  Hornhlende  Schist  correspond  to  common 
Gneiss  and  Mica  Schist,  hornblende  taking  the  place  of 
mica. 

The  Yolcaxic  Series 
C07isisting   of  Feldspar,   Amphibole   or    Pyroxene,   and 
Zeolites. 

©lorite  is  a  compact,  tough,  and  heavy  rock,  common- 
ly greenish-black,  brownish-black,  or  grayish-black  in 
color.  It  contains  amphibole,  but  no  pyroxene,  and  is 
an  ancient  lava. 

Dolerite  or  Trap  in  the  fine-grained  varieties  is  scarcely 
to  be  distinguished  from  Diorite  by  the  appearance,  and  is 
well  exhibited  in  the  Palisades  of  the  Hudson  and  the 
East  and  West  Rocks  of  Kew  Haven.  It  contains  pyrox- 
ene in  place  of  amphibole. 

Basalt  is  like  dolerite,  but  contains  grains  of  chrysolite. 
The  recent  lavas  of  volcanic  regions  are  commonly  basaltic 
in  composition,  though  very  light  and  porous  in  texture. 

Porpliyryi — Associated  with  basalt  occur  some  feld- 
spathic  lavas,  of  which  porphyry  is  common.  It  consists 
of  a  compact  base  of  feldspar,  with  disseminated  crystals 
of  feldspar  usually  lighter  in  color  than  the  mass  of  the 
rock. 

•   Pumice  is  a  vesicular  rock,  having  nearly  the  composi- 
tion of  feldspar. 

The  Mag]s-esia:n-  Series 
consisting  of  Quartz,  Feldspar  and  Talc,  or  Chlorite. 

Talcose  Granite  differs  from  common  granite  in  the 
substitution  of  talc  for  mica.     Is  a  fragile  and  more  easily 


OP.IGIX    AK'D    FOEMATIOX    OF    SOILS.  121 

decomposable  rock  than  granite.    It  passes  through  talcose 
gneiss  into 

Talcose  Schistj  which  resembles  mica-schist  in  colors 
and  in  facihty  of  splitting  into  slabs,  but  has  a  less  glis- 
tening luster  and  a  soapy  feel. 

Clllorltic  Schist  resembles  talcose  schist,  but  has  a  less 
mictuous  feel,  and  is  generally  of  a  dark  green  color. 

Related  to  the  above  are  Steatite^  or  soapstone^ — nearly 
pure,  granular  talc;  and  Serpentine  rockj  consisting 
chiefly  of  serpentine. 

The  above  are  the  more  common  and  wide-spread  si- 
licious  rocks.  By  the  blending  together  of  the  different 
members  of  each  series,  and  the  related  members  of  the 
different  series,  and  by  the  introduction  of  other  minerals 
into  their  composition,  an  almost  endless  variety  of  si- 
licious  rocks  has  been  produced.     Turning  now  to  the 

Crystalline  Calcareous  Rocks,  we  have 

l»rafflular  Limestone,  consisting  of  a  nearly  pure  car- 
bonate of  lime,  in  more  or  less  coarse  grains  or  crystals, 
commonly  white  or  gray  in  color,  and  having  a  glistening 
luster  on  a  freshly  broken  surface.  Tlie  finer  kinds  are 
employed  as  monumental  marble. 

Dolomite  has  all  the  appearance  of  granular  limestone, 
but  contains  a  large  (variable)  amount  of  carbonate  of 
magnesia. 

The  Feagmental  or  Sedimentary  Rocks  are  as  fol- 
lows: 

Conglomerates  have  resulted  from  the  consolidation  of 
rather  coarse  fragments  of  any  kind  of  rock.  According 
to  the  nature  of  the  materials  composing  them,  they  may 
be  granitic^  syevAtic^  calcareous^  basaltic^  etc.,  etc.  The'y 
pass  into 

Sandstones?  which  consist  of  small  fragments  (sand), 
are  generally  siliciovs  in  character,  and  often  are  nearly 
6 


122  HOW    CROPS    FEED. 

pure  quartz.  The  freestone  of  the  Connecticut  Valley  is 
a  granitic  sandstone,  containing  fragments  of  feldspar 
and  spangles  of  mica. 

Other  varieties  are  calcareous^  argillaceous  {clayey)^ 
basaltic^  etc.,  etc. 

Shales  are  soft,  slaty  rocks  of  various  colors,  gray,  green, 
red,  blue,  and  black.  They  consist  of  compacted  clay. 
When  crystallized  by  metamorphic  action,  they  constitute 
argillite. 

LlMCStOBCS  of  the  sedimentary  kind  are  soft,  compact, 
nearly  liisterless  rocks  of  various  colors,  usually  gray, 
blue,  or  black.  They  are  sometimes  nearly  pure  carbon- 
ate of  lime,  but  usually  contain  other  substances,  and  are 
often  highly  impure.  When  containing  much  carbonate 
of  magnesia  they  are  termed  magnesian  Ur/iestones.  They 
joass  mto  sandstones  through  intermediate  calciferous 
sand  rocJcs^  and  into  shales  through  argillaceous  lime- 
stones. These  impure  limestones  furnish  the  hydraulic 
cements  of  commerce. 


CONVERSION  OF  ROCKS  INTO  SOILS. 

Soils  are  broken  and  decomposed  rocks.  We  find  in 
nearly  all  soils  fragments  of  rock,  recognizable  as  such  by 
the  eye,  and  by  help  of  the  microscope  it  is  often  easy  to 
perceive  that  those  portions  of  the  soil  which  are  impalpa- 
ble to  the  feel  chiefly  consist  of  minuter  grains  of  the  same 
rock. 

Geology  makes  j^robable  that  the  globe  was  once  in  a 
melted  condition,  and  came  to  its  present  state  through  a 
process  of  cooling.  By  loss  of  heat  its  exterior  surface 
solidified  to  a  crust  of  solid  rock,  totally  incapable  of  sup- 
porting the  life  of  agricultural  plants,  being  impenetrable 
to  their  roots,  and  destitute  of  all  the  other  external  char- 
acteristics of  a  soil. 


OKIGI^iT    AND    FOEMATION    OF    SOILS.  123 

The  first  step  towards  the  formation  of  a  soil  must  have 
been  the  pulverization  of  the  rock.  This  has  been  accom- 
plished by  a  variety  of  agencies  acting  through  long  pe- 
riods of  time.  The  causes  which  could  produce  such  re- 
sults are  indeed  stupendous  when  contrasted  with  the 
narrow  experience  of  a  single  human  life,  but  are  really 
trifling  compared  with  the  magnitude  of  the  earth  itself, 
for  the  soil  fonns  upon  the  surface  of  our  globe,  whose  di- 
ameter is  nearly  8,000  miles,  a  thin  coating  of  dust,  meas- 
ured in  its  greatest  accumulations  not  by  miles,  nor 
scarcely  by  rods,  but  by  feet. 

The  conversion  of  rocks  to  soils  has  been  performed, 
1st,  by  Changes  of  Temperature ;  2d,  by  Moving  Water 
or  Ice  ;  3d,  by  the  Chemical  Action  of  Water  and  Air  ; 
4th,  by  the  Influence  of  Yegetahle  and  Animcd  life. 

1. — Chai^^ges  of  TeMPEEATUPvE. 

The  continued  cooling  of  the  globe  after  it  had  become 
enveloped  in  a  solid  rock-crust  must  have  been  accom- 
panied by  a  contraction  of  its  volume.  One  effect  of  this 
shrinkage  would  have  been  a  subsidence  of  portions  of 
the  crust,  and  a  wrinkling  of  other  portions,  thus  produc- 
ing on  the  one  hand  sea-basins  and  valleys,  and  on  the 
other  mountain  ranges.  Another  effect  would  have  been 
the  cracking  of  the  crust  itself  as  the  result  of  its  own 
contraction. 

The  pressure  caused  by  contraction  or  by  mere  weight 
of  superincumbent  matter  doubtless  led  to  the  production 
of  the  laminated  structure  of  slaty  rocks,  which  may  be 
readily  imitated  in  wax  and  clay  by  aid  of  an  hydraulic 
press.  Basaltic  and  trap  rocks  in  cooling  from  fusion  often 
acquire  a  tendency  to  separate  into  vertical  columns, 
somewhat  as  moist  starch  splits  into  five  or  six-sided  frag- 
ments, when  dried.  These  columns  are  again  transversely 
jointed.  The  Giant's  Causeway  of  Ireland  is  an  illustra- 
tion. These  fractures  and  joints  are,  perhaps,  the  first  oc- 
casion of  the  breaking:  down  of  the  rocks.     The  fact  that 


124  HOW    CROPS    FEED. 

many  rocks  consist  of  crystalline  grains  of  distinct  min- 
erals more  or  less  intimately  blended,  is  a  point  of  weak- 
ness in  their  structure.  The  grains  of  quartz,  feldspar, 
and  mica,  of  a  granite,  when  exposed  to  changes  of  tem- 
perature, must  tend  to  separate  from  each  other;  because 
the  extent  to  which  they  expand  and  contract  by  alterna- 
tions of  heat  and  cold  are  not  absolutely  equal,  and  be- 
cause, as  Senarmont  has  proved,  the  same  crystal  expands 
or  contracts  unequally  in  its  diiferent  diameters. 

Action  of  Freezing  Water. — It  is,  however,  when  wa- 
ter insinuates  itself  into  the  slight  or  even  imperceptible 
rifts  thus  opened,  and  then  freezes,  that  the  process  of  dis- 
integration becomes  more  rapid  and  more  vigorous.  Wa- 
ter in  the  act  of  conversion  into  ice  expands  tV  of  its  bulk, 
and  the  force  thus  exerted  is  sufficient  to  burst  vessels  of 
the  strongest  materials.  In  cold  latitudes  or  altitudes  this 
agency  working  through  many  years  accomplishes  stupen- 
dous results. 

The  adventurous  explorer  in  the  higher  Swiss  Alps  fre- 
quently sees  or  hears  the  fall  of  fragments  of  rock  thus 
loosened  from  the  peaks. 

Along  the  base  of  the  vertical  trap  cliffs  of  'New  Haven 
and  the  Hudson  River,  lie  immense  masses  of  broken  rock 
reaching  to  more  than  half  the  height  of  the  bluffs  them- 
selves, rent  off  by  this  means.  The  same  cause  operates 
in  a  less  conspicuous  but  not  less  important  way  on  the 
surface  of  the  stone,  loosening  the  minute  grains,  as  in 
the  above  instances  it  rends  off  enormous  blocks.  A 
smooth,  clean  pebble  of  the  very  compact  Jura  limestone, 
of  such  kind,  for  example,  as  abound  in  the  rivers  of 
South  Bavaria,  if  moistened  with  water  and  exposed  over 
night  to  sharp  frost,  on  thawing,  is  muddy  with  the  de- 
tached particles. 

2. — Moving  ¥t^ater  oe  Ice. 

Changes  of  temperature  not  only  have  created  differ- 
ences of  level  in  the  earth's  surface,  but  they  cause  a  con- 


ORIGIX    AND    FORMATIOX    OP    SOILS.  125 

tinual  transfer  of  water  from  lower  to  higher  levels.  The 
elevated  lands  are  cooler  than  the  valleys.  In  their  re- 
gion occurs  a  continual  condensation,  of  vapor  from  the 
atmosphere,  vfhich  is  as  continually  supplied  from  the 
heated  valleys.  In  the  mountains,  thus  begin,  as  rills,  the 
streams  of  water,  which,  gathering  volume  in  their  descent, 
unite  below  to  vast  rivers  that  flow  unceasingly  into  the 
ocean. 

These  streams  score  their  channels  into  the  firmest  rocks. 
Each  grain  of  loosened  material,  as  carried  downward  by 
the  current,  cuts  the  rock  along  which  it  is  dragged  so 
long  as  it  is  in  motion. 

The  sides  of  the  channel  being  undermined  and  loosen- 
ed by  exposure  to  the  frosts,  fall  into  the  stream.  In  time 
of  floods,  and  always,  when  the  path  of  the  river  has  a 
rapid  descent,  the  mere  momentum  of  the  water  acts  pow- 
erfully upon  any  inequalities  of  surface  that  oppose  its 
course,  tearing  away  the  rocky  walls  of  its  channel.  The 
blocks  and  grains  of  stone,  thus  set  in  motion,  grind  each 
other  to  smaller  fragments,  and  when  the  turbid  waters 
clear  themselves  in  a  lake  or  estuary,  there  results  a  bed 
of  gravel,  sand,  or  soil.  Two  hundred  and  sixty  years 
ago,  the  bed  of  the  Sicilian  river  Simeto  was  obstructed  by 
the  flow  across  it  of  a  stream  of  lava  from  Etna.  Since 
that  time  the  river,  with  but  slight  descent,  has  cut  a  chan- 
nel through  this  hard  basalt  from  fifty  to  several  hundred 
feet  wide,  and  in  some  parts  forty  to  fifty  deep. 

But  the  action  of  water  in  j)nlverizing  rock  is  not  com- 
pleted when  it  reaches  the  sea.  The  oceans  are  in  j^erpet- 
ual  agitation  from  tides,  wind-waves,  and  currents  like 
the  Gulf-stream,  and  work  continual  changes  on  their 
shores. 

Glaciers, — What  happens  from  the  rapid  flow  of  water 
down  the  sides  of  mountain  slopes  below  the  frost-line  is 
also  true  of  the  streams  of  ice  which  more  slowly  descend 
from  the  frozen  summits.     The  glaciers  appear  like  motion- 


123  HOW    CHOPS    FEED. 

less  ice-fields,  but  they  are  frozen  rivers,  rising  in  perpet* 
ual  snows  and  melting  into  water,  after  having  reached 
half  a  mile  or  a  mile  below  the  limits  of  frost.  The  snow 
that  accumulates  on  the  frozen  peaks  of  high  mountains, 
which  are  bathed  by  moist  winds,  descends  the  slopes  by 
its  own  weight.  The  rate  of  descent  is  slow, — a  few 
inches,  or,  at  the  most,  a  few  feet,  daily.  The  motion  it- 
self is  not  continuous,  but  intermittent  by  a  succession  of 
pushes.  In  the  gorges,  where  many  smaller  glaciers  unite, 
the  mass  has  often  a  depth  of  a  mile  or  more.  Under  the 
pressure  of  accumulation  the  snow  is  compacted  to  ice. 
Mingled  with  the  snows  are  masses  of  rock  broken  off 
the  higher  pinnacles  by  the  weight  of  adhering  ice,  or 
loosened  by  alternate  freezing  and  thawing,  below  the  line 
of  perpetual  frost.  The  rocks  thus  falling  on  the  edge  of 
a  glacier  become  a  part  of  the  latter,  and  partake  its  mo- 
tion. "When  the  moving  mass  bends  over  a  convex  sur- 
face, it  cracks  vertically  to  a  great  depth.  Into  the  cre- 
vasses thus  formed  blocks  of  stone  fall  to  the  bottom,  and 
water  melted  from  the  surface  in  hot  days  flows  down  and 
finds  a  channel  beneath  the  ice.  The  middle  of  the  glacier 
moves  most  rapidly,  the  sides  and  bottom  being  retarded 
by  friction.  The  ice  is  thus  rubbed  and  rolled  upon  itself, 
and  the  stones  imbedded  in  it  crush  and  grind  each  other 
to  smaller  fragments  and  to  dust.  The  rocky  bed  of  the 
glacier  is  broken,  and  ploughed  by  the  stones  frozen  into 
its  sides  and  bottom.  The  glacier  thus  moves  until  it 
descends  so  low  that  ice  cannot  exist,  and  gradually  dis- 
solves into  a  torrent  whose  waters  are  always  thick  with 
mud,  and  whose  course  is  strewn  with  worn  blocks  of 
stone  (boulders)  for  many  miles. 

The  Rhone,  which  is  chiefly  fed  from  the  glaciers  of  the 
Alps,  transports  such  a  volume  of  rock-dust  that  its  muddy 
waters  may  be  traced  for  six  or  seven  miles  after  they 
have  poured  themselves  into  the  Mediterranean. 

3. — Chemicai.  Action  of  Watek  and  Aik. 


ORIGIN    AND    FORMATION    OP    SOILS.  127 

Water  acts  chemically  upon  rocks,  or  rather  upon  their 
constituent  minerals,  in  two  ways,  viz.,  hy  Combination 
and  Solution. 

Hydration, — By  chemically  uniting  itself  to  the  mineral 
or  to  some  ingredient  of  the  mineral,  there  is  formed  in 
many  instances  a  new  compound,  Avhich,  by  being  softer 
and  more  bulky  than  the  original  substance,  is  the  first 
step  towards  further  change.  Mica,  feldspar,  amphibole, 
and  pyroxene,  are  minerals  which  have  been  artificially 
produced  in  the  slags  or  linings  of  smelting  furnaces,  and 
thus  formed  they  have  been  found  totally  destitute  of  wa- 
ter, as  might  be  expected  from  the  high  temperature  in 
which  they  originated.  Yet  these  minerals  as  occurring 
in  nature,  even  when  broken  out  of  blocks  of  apparently 
unaltered  rock,  and  especially  when  they  have  been  di- 
rectly exposed  to  the  weather,  often,  if  not  always,  con- 
tain a  small  amount  of  water,  in  chemical  combination 
(water  of  hydration). 

Solution. — As  a  solvent,  water  exercises  the  most  im- 
portant influence  in  disintegrating  minerals.  Apatite, 
when  containing  much  chlorine,  is  gradually  decomposed 
by  treatment  with  water,  chloride  of  calcium,  which  is 
very  soluble,  being  separated  from  the  nearly  insoluble 
phosphate  of  lime.  The  minerals  which  compose  silicious 
rocks  are  all  acted  on  perceptibly  by  pure  water.  This  is 
readily  observed  when  the  minerals  are  employed  in  the 
state  of  fine  powder.  If  pulverized  feldspar,  amphibole, 
etc.,  are  simply  moistened  with  pure  water,  the  latter  at 
once  dissolves  a  trace  of  alkali,  as  shown  by  its  turning 
red  litmus-paper  blue.  This  solvent  action  is  so  slight 
upon  a  smooth  mass  of  the  mineral  as  hardly  to  be  per- 
ceptible, because  the  action  is  limited  by  the  extent  of 
surface.  Pulverization,  which  increases  the  surface  enor- 
mously, increases  the  solvent  effect  in  a  similar  proportion. 
A  glass  vessel  may  have  water  boiled  in  it  for  hours  with- 
out its  luster  being  dimmed  or  its  surface  materially  acted 


128  now  csops  feed. 

upon,  whereas  the  same  glass  '^  finely  pulverized  is  attack- 
ed by  water  so  readily  as  to  give  at  once  a  solution  alka- 
line to  the  taste.  Messrs.  W.  B.  and  R.  E.  Rogers  {Am. 
Jour.  Sci.,  V,  404, 1848)  found  that  by  continued  digestion 
of  pure  water  for  a  week,  with  powdered  feldspar,  horn- 
blende, chlorite,  serpentine,  and  natrolite,f  these  minerals 
yielded  to  the  solvent  from  0.4  to  1  per  cent  of  their 
weight. 

In  nature  we  never  deal  with  pure  water,  but  with  wa- 
ter holding  in  solution  various^  matters,  either  derived 
from  the  air  or  from  the  soil.  These  substances  modify, 
and  in  most  cases  enhance,  the  solvent  power  of  water. 

Action  of  Carboiiic  Acid. — This  gaseous  substance  is 
absorbed  by  or  dissolved  in  all  natural  waters  to  a  greater 
or  less  extent.  At  common  temperatures  and  pressure 
water  is  capable  of  taking  up  its  own  bulk  of  the  gas. 
At  lower  temperatures,  and  under  increased  pressure,  the 
quantity  dissolved  is  much  greater.  Carbonated  loater^ 
as  we  may  designate  this  solution,  has  a  high  solvent 
power  on  the  carbonates  of  lime,  magnesia,  protoxide  of 
iron,  and  protoxide  of  manganese.  The  salts  just  named 
are  as  good  as  insoluble  in  pure  water,  but  they  exist  in 
considerable  quantities  in  most  natural  waters.  The 
spring  and  well  waters  of  limestone  regions  are  hard  on 
account  of  their  content  of  carbonate  of  lime.  Chalyb- 
eate waters  are  those  which  hold  carbonate  of  iron  in 
solution.  When  carbonated  water  comes  in  contact  with 
silicious  minerals,  these  are  decomposed  much  more  rapidly 
than  by  pure  w-ater.  The  lime,  magnesia,  and  iron  they 
contain,  are  partially  removed  in  the  form  of  carbonates. 

Struve  exposed  powdered  phonolite  (a  rock  composed 
of  feldspar  and  zeolites)  to  water  saturated  w^ith  carbonic 


*  Glass  is  a  silicate  of  potash  or  soda, 
t  Mesotype. 


ORIGIN   AND   FORMATION    OF    SOILS.  129 

acid  under  a  pressure  of  3  atmosj^heres,  and  obtained  a 
solution  of  which  a  pound  *  contained : 


Carbonate  of  soda, 

22.0 

grains. 

Chloride  of  sodium, 

2.0 

Sulphate  of  potash. 

1.7 

''   soda, 

4.8 

Carbonate  of  lime, 

4.5 

"          "   magnesia, 

1.1 

Silica, 

0.5 

Phosohoric  acid  and  manganese, 

traces 

Total, 

37.1  , 

grains. 

In  various  natural  springs,  water  comes  to  the  surface 
so  charged  with  carbonic  acid  that  the  latter  escapes 
copiously  in  bubbles.  Such  waters  dissolve  large  quantities 
of  mineral  matters  from  the  rocks  through  which  they 
emerge.  Examples  are  seen  in  the  springs  at  Saratoga, 
I*^.  Y.  According  to  Prof.  Chandler,  the  "  Saratoga 
Spring,"  whose  waters  issue  directly  from  the  rock,  con- 
tains in  one  gallon  of  231  cubic  inches  : 

grains. 


Cliloride  of  Sodium  (common  salt) 

398. 3G1  . 

"        "   Potassium, 

9.698 

Bromide  of  Sodium, 

0.571 

Iodide  of  Sodium, 

0.126 

Sulphate  of  Potash, 

5.400 

Carbonate  of  Lime, 

86.483 

"        "  Magnesia, 

41.050 

"         "  Soda, 

8.948 

"         "  Protoxide  of 

iron, 

.879 

Silica, 

1.283 

Phosphate  of  lime, 

Solid  matters. 

trace 

552. 7Q9 

Carbonic  acid  gas,  (407.647 

cubic  inches  at 

53' 

'  Fah.) 

Water, 

58,317.110 

The  waters  of  ordinary  springs  and  rivers,  as  well  as 
those  that  fall  upon  the  earth's  surface  as  rain,  are,  indeed, 


*  The  Saxon  pound  contains  7,680  Saxon  grains. 

6* 


130 


HOW    CROPS    FEED. 


by  no  means  fully  charged  with  carbonic  acid,  and  their 
solvent  effect  is  much  less  than  that  exerted  by  water  sat- 
urated with  this  gas. 

The  quantity  (by  volume)  of  carbonic  acid  in  10,000 
parts  of  rain-water  has  been  observed  as  follows :  Accord- 
ing to 

Locality. 
Lampadius,  8  Country  near  Freiberg,  Saxony, 

Mulder,  20  City  of  UtrecM,  Holland. 

Von  Baumhauer,  40  to  90        "     "         u  u 

Peligot,  5  ? 

The  quantities  found  are  variable,  as  might  be  expected, 
and  we  notice  that  the  largest  proportion  above  cited  does 
not  even  amount  to  one  per  cent. 

In  river  and  spring  water  the  quantities  are  somewhat 
larger,  but  the  carbonic  acid  exists  chiefly  in  chemical  com- 
bination as  bicarbonates  of  lime,  magnesia,  etc. 

In  the  capillary  water  of  soils  containing  much  organic 
matters,  more  carbonic  acid  is  dissolved.  According  to  a 
single  observation  of  De  Saussure's,  such  water  contains 
2° 1 0  of  the  gas.  In  a  subsequent  paragraph,  p.  221,  is 
given  the  reason  of  the  small  content  of  carbonic  acid  in 
these  waters. 

The  weaker  action  of  these  dilute  solutions,  when  con- 
tinued through  long  periods  of  time  and  extending  over 
an  immense  surface,  nevertheless  accomplishes  results  of 
vast  significance. 

Solutions  of  Alkali-Salts. — Rain-water,  as  we  have 
already  seen,  contains  a  minute  quantity  of  salts  of  am- 
monia (nitrate  and  bicarbonate).  The  water  of  springs 
and  rivers  acquires  from  the  rocks  and  soil,  salts  of  soda 
and  potash,  of  lime  and  magnesia.  These  solutions,  dilute 
though  they  are,  greatly  surpass  pure  water,  or  even  car- 
bonated water,  in  their  solvent  and  disintegrating  action. 
Phosphate  of  lime,  the  earth  of  bones,  is  dissolved  by 
pure  water  to  an  extent  that  is  hardly  appreciable ;   in 


ORIGT2T   AND    FORMATION    OF    SOILS.  131 

salts  of  ammonia  and  of  soda,  however,  it  is  taken  up  in 
considerable  quantity.  Solution  of  nitrate  of  ammonia 
dissolves  lime  and  magnesia  and  their  carbonates  with 
great  ease.  In  general,  up  to  a  certain  limit,  a  saline  so- 
lution acquires  increased  solvent  power  by  increase  in  the 
amount  and  number  of  dissolved  matters.  This  import- 
ant fact  is  one  to  which  we  shall  recur  at  another  time. 

Action  of  Oxygen. — This  element,  the  great  mover  of 
chemical  changes,  which  is  present  so  largely  in  the  at- 
mosphere, has  a  strong  tendency  to  unite  with  certain 
bodies  which  are  almost  universally  distributed  in  the 
rocks.  On  turning  to  the  analyses  of  minerals,  p.  110,  we 
notice  in  nearly  every  instance  a  quantity  of  protoxide  of 
iron,  or  protoxide  of  manganese.  The  green,  dark  gray, 
or  black  minerals,  as  the  micas,  amphibole,  pyroxene, 
chlorite,  talc,  and  serpentine,  invariably  contain  these  prot- 
oxides in  notable  proportion.  In  the  feldspars  they  exist, 
indeed,  in  very  minute  quantity,  but  are  almost  never  en- 
tirely wanting.  Sulphide  of  iron  (iron  pyrites),  in  many 
of  its  forms,  is  also  disposed  to  oxidize  its  sulphur  to  sul- 
phuric acid,  its  iron  to  sesquioxide,  and  this  mineral  is 
widely  distributed  as  an  admixture  in  many  rocks.  In 
tra])  or  basaltic  rocks,  as  at  Bergen  Hill,  metallic  iron  is 
said  to  occur  in  minute  proportion,*  and  in  a  state  of  fine 
division.  The  oxidation  of  these  substances  materially 
hastens  the  disintegration  of  the  rocks  containing  them, 
since  the  higher  oxides  of  iron  and  of  manganese  occupy 
more  space  than  the  metals  or  lower  oxides.  This  fact  is 
well  illustrated  by  the  sulphate  of  protoxide  of  iron  (cop- 
peras, or  green-vitriol),  which,  on  long  keeping,  exposed  to 
the  air,  is  converted  from  transparent,  glassy,  green  crys- 
tals to  a  bulky,  brown,  opaque  powder  of  sulphate  of 
sesquioxide  of  iron. 

Weattiering'e — The  conjoined  influence  of  water,  car- 


*  This  statement  rests  on  the  authority  of  Professor  Henry  Wurtz,  of  New  York. 


132  HOW    CSOPS    FEED. 

bonic  acid,  oxygen,  and  the  salts  held  in  solution  by  the 
atmospheric  waters,  is  expressed  by  the  word  v^eathering. 
This  term  may  likewise  include  the  action  of  frost. 

When  rocks  weather,  they  are  decomposed  or  dissolved, 
and  new  compounds,  or  new  forms  of  the  original  mat- 
ter, result.  The  soil  is  a  mixture  of  broken  or  pulverized 
rocks,  with  the  products  of  their  alteration  by  weathering. 

a.  Weatlierliig  of  Quarts  Eock, — Quartz  (silicic  acid), 
as  occurring  nearly  pure  in  quartzite,  and  in  many  sand- 
stones, or  as  a  chief  ingredient  of  all  the  granitic,  horn- 
blendic,  and  many  other  rocks,  is  so  exceedingly  hard  and 
insohible,  that  the  lifetime  of  a  man  is  not  sufficient  for 
the  direct  observation  of  any  change  in  it,  when  it  is  ex- 
posed to  ordinary  weathering.  It  is,  in  fact,  the  least 
destructible  of  the  mineral  elements  of  the  globe.  JSTever- 
theless,  quartz,  even  when  pure,  is  not  absolutely  insoluble, 
particularly  in  water  containing  alkali  carbonates  or  sili- 
cates. In  its  less  pure  varieties,  and  especially  when  as- 
sociated with  readily  decomposable  minerals,  it  is  acted 
on  more  rapidly.  The  quartz  of  granitic  rocks  is  usually 
roughened  on  the  surface  when  it  has  long  been  exposed 
to  the  weather. 

h.  Tlie  Feldspars  weather  much  more  easily  than 
quartz,  though  there  are  great  differences  among  them. 
The  soda  and  lime  feldspars  decompose  most  readily, 
while  the  potash  feldspars  are  often  exceedingly  durable. 
The  decomposition  results  in  completely  breaking  up  the 
hard,  glassy  mineral.  In  its  place  there  remains  a  white 
or  yellowish  mass,  which  is  so  soft  as  to  admit  of  crush- 
ing between  the  fingers,  and  which,  though  usually,  to  the 
naked  eye,  opaque,  and  non-crystalhne,  is  often  seen,  under 
a  powerful  magnifier,  to  contain  numerous  transparent  crys- 
talline plates.  The  mass  consists  principally  of  the  crys- 
talline mineral,  haollnite^  a  hydrated  silicate  of  alumina,  (the 
analysis  of  which  has  been  given  already,  p.  113,)  mixed 


ORIGIN   AXD    FOSMATION    OF    SOILS.  133 

with  hydrated  silica,  and  often  witii  grains  of  undecompos- 
ed  mineral.  If  we  compare  the  composition  of  pure  pot- 
ash feldspar  with  that  of  kaolinite,  assuming,  what  is 
probably  true,  that  all  the  alumina  of  the  former  remains 
in  the  latter,  we  find  what  portions  of  the  feldspar  have 
been  removed  and  washed  away  by  the  water,  which,  to- 
gether with  carbonic  acid,  is  the  agent  of  this  change. 

Feldspar.  Kaolinite.  Liberated.        Added. 

Alumina 18.3  18.3  0 

Silica 64.8  23.0  41.8 

Potash 16.9  16.9 

Water 6.4  6.4 

100  47.7  58.7  ~QA 

It  thus  appears  that,  in  the  complete  conversion  of  100 
parts  of  potash  feldspar  into  kaolinite,  there  result  47.7 
parts  of  the  latter,  while  58.7° J^  of  the  feldspar,  viz : 
41.8°  lo  of  silica  and  16.9°  1^  of  potash,  are  dissolved  out. 

The  potash,  and,  in  case  of  other  feldspars,  soda,  lime, 
and  magnesia,  are  dissolved  as  carbonates.  If  much  water 
has  access  during  the  decomposition,  all  the  liberated  silica 
is  carried  away.*  It  usually  happens,  however,  that  a  por- 
tion of  the  silica  is  retained  in  the  kaolin  (perhaps  in  a 
manner  similar  to  that  in  which  bone  charcoal  retains  the 
coloring  matters  of  crude  sugar).  The  same  is  true  of  a 
portion  of  the  alkali,  lime,  and  oxide  of  iron,  which  may 
have  existed  in  the  original  feldspar. 

The  formation  of  kaolin  may  be  often  observed  in  na- 
ture. In  mines,  excavated  in  feldspathic  rocks,  the  fis- 
sures and  cavities  through  which  surface  water  finds  its 
way  downwards  are  often  coated  or  filled  with  this  sub- 
stance. 

c.  Other  Silkioiis  Miaerals?  as  Leucite,  (Topaz,  Scapo- 
lite,)  etc.,  yield  kaolin  by  decomposition.  It  is  probable 
that  the  micas,  which  decompose  with  difficulty,  (phlogo- 

*  We  have  seen  (H.  C.  G.,  p.  121)  that  silica,  when  newly  set  free  from  combi- 
nation, is,  at  first,  freely  soluble  in  water. 


134  HOW    CEOPS    FEED. 

pite,  perhaps,  excepted,)  and  the  amphiboles  and  pyrox= 
enes,  which  are  often  easily  disintegrated,  also  yield 
kaolin  ;  but  in  the  case  of  these  latter  minerals,  the  result- 
ing kaolinite  is  largely  mixed  with  oxides  and  silicates  of 
iron  and  manganese,  so  that  its  properties  are  modified, 
and  identification  is  difficult.  Other  hydrated  silicates  of 
alumina,  closely  allied  to  kaolinite,  appear  to  be  formed  in 
the  decomposition  of  compound  silicates. 

Ordinary  Clays,  as  pipe-clay,  blue-clay,  brick-clay,  etc., 
are  mixtures  of  kaolinite,  or  of  a  similar  hydrated  silicate 
of  alumina,  with  a  variety  of  other  substances,  as  free 
silica,  oxides,  and  silicates  of  iron  and  manganese,  carbon- 
ate of  lime,  and  fragments  or  fine  powder  of  undecom- 
posed  minerals.  Fresenius  deduces  from  his  analyses  of 
several  ISTassau  clays  the  existence  in  them  of  a  compound 
having  the  symbol  Al^  O3  3  SiO^+H^O,  and  the  follow- 
ing composition  ^er  cent. 

Silica,  57.14 

Alumina,        31.72 
Water,  11.14 


100.00 


Other  chemists  have  assumed  the  existence  of  hydrated 
silicates  of  alumina  of  still  difterent  composition  in  clays, 
but  kaolinite  is  the  only  one  which  occurs  in  a  pure  state, 
as  indicated  by  its  crystallization,  and  the  existence  of 
the  others  is  not  perfectly  established.  (S.  W.  Johnson 
and  J.  M.  Blake  07i  Kaolinite^  ete.^  Am.  Jour.  Sci.^  May^ 
1867,  pp.  351-362.) 

d.  The  Zeolites  readily  suffer  change  by  weathering ; 
little  is  known,  however,  as  to  the  details  of  their  disinte- 
gration. Instead  of  yielding  kaolinite,  they  appear  to  be 
transformed  into  other  zeolites,  or  retain  something  of  their 
original  chemical  constitution,  although  mechanically  dis- 
integrated or  dissolved.     We  shall  see  hereafter  that  there 


OEIGI?^  AND   FOEMATION   OF   SOILS.  135 

is  strong  reason  to  assume  the  existence  of  compounds 
analogous  to  zeolites  in  every  soil. 

e.  Serpentine  and  Magneslan  Silicates  are  generally 
slow  of  decomposition,  and  yield  a  meager  soil. 

/.  The  Limestones,  when  pure  and  compact,  are  very 
durable :  as  they  become  broken,  or  when  impure,  they 
often  yield  rapidly  to  the  weather,  and  impregnate  the 
streams  which  flow  over  them  with  carbonate  of  lime. 

g,  Argillite  and  Argillaceous  Limestones,  which  have 
resulted  from  the  solidification  of  clays,  readily  yield  clay 
again,  either  by  simple  pulverization  or  by  pulverization 
and  weathering,  according  as  they  have  suflfered  more  or 
less  change  by  metamorphism. 


5. 


INCORPORATION  OF  ORGANIC  MATTER  WITH  THE  SOIL  AND 
ITS  EFFECTS. 

Antiquity  of  Vegetation. — Geological  observations  lead 
to  the  conclusion  that  but  small  portions  of  the  earth's 
surface-rocks  were  formed  previous  to  the  existence  of 
vegetation.  The  enormous  tracts  of  coal  found  in  every 
quarter  of  the  globe  are  but  the  residues  of  preadamite 
forests,  while  in  the  oldest  stratified  rocks  the  remains  of 
plants  (marine)  are  either  most  distinctly  traced,  or  the 
abundance  of  animal  forms  warrants  us  in  assumino^  the 
existence  of  vegetation  previous  to  their  deposition. 

The  Development  of  Vegetation  on  a  purely  Mineral 
Soil. — The  mode  in  which  the  original  inorganic  soil  be- 
came more  or  less  impregnated  with  organic  matter  may 
be  illustrated  by  what  has  happened  in  recent  years  upon 
the  streams  of  lava  that  have  issued  from  volcanoes.  The 
lava  flows  from  the  crater  as  red-hot  molten  rock,  often  in 
masses  of  such  depth  and  extent  as  to  require  months  to 
cool  down  to  the  ordinary  temperature.     For  many  years 


136  HOW    CROPS    FEED. 

the  lava  is  incapable  of  bearing  any  vegetation  save  some 
almost  microscopic  forms.  During  these  years  the  surface 
of  the  rock  suffers  gradual  disintegration  by  the  agencies 
of  air  and  water,  and  so  in  time  acquires  the  power  to 
support  some  lichens  that  appear  at  first  as  mere  stains 
upon  its  surface.  These,  by  their  decay,  increase  the 
film  of  soil  from  which  they  sprung.  The  growth  of 
new  generations  of  these  plants  is  more  and  more  vigor- 
ous, and  other  superior  kinds  take  root  among  them. 
After  another  period  of  years,  there  has  accumulated  a 
tangible  soil,  supporting  herbaceous  plants  and  dwarf 
shrubs.  Henceforward  the  increase  proceeds  more  rapid- 
ly ;  shrubs  gradually  give  place  to  trees,  and  in  a  century, 
more  or  less,  the  once  hard,  barren  rock  has  weathered  to 
a  soil  fit  for  vineyards  and  gardens. 

Those  lowest  orders  of  plants,  the  lichens  and  mosses, 
which  prepare  the  way  for  forests  and  for  agricultural 
vegetation,  are  able  to  extract  nourishment  from  the  most 
various  and  the  most  insoluble  rocks.  They  occur  abund- 
antly on  all  our  granitic  and  schistose  rocks.  Even  on 
quartz  they  do  not  refuse  to  grow.  The  white  'quartz 
hills  of  Berkshire,  Massachusetts,  are  covered  on  their 
moister  northern  slopes  with  large  patches  of  a  leathery 
lichen,  which  adheres  so  firmly  to  the  rock  that,  on  being 
forced  off,  particles  of  the  stone  itself  are  detached.  Many 
of  the  old  marbles  of  Greece  are  incrusted  with  oxalate 
of  lime  left  by  the  decay  of  lichens  which  have  grown 
upon  their  surface. 

Illimus. — By  the  decay  of  successive  generations  of 
plants  the  soil  gradually  acquires  a  certain  content  of  dead 
organic  matter.  The  falling  leaves,  seeds  and  stems  of 
vegetation  do  not  in  general  waste  from  the  surface  as 
rapidly  as  they  are  renewed.  In  forests,  pastures,  prai- 
ries, and  marshes,  there  accumulates  on  the  surface  a  brown 
or  black  mass,  termed  hunms,  of  which  leaf-mold,  swamp- 
muck,  and  peat  are  varieties,  differing  in  appearance  as  in 


OEIGES-   AND    F0KMATI0I5    OF    SOILS.  137 

the  circumstances  of  their  origin.  In  the  depths  of  the 
soil  similar  matters  are  formed  by  the  decay  of  roots  and 
other  subterranean  parts  of  plants,  or  by  the  inversion  of 
sod  and  stubble,  as  well  as  by  manuring. 

Decay  of  Vegetatl©a» — When  a  plant  or  any  part  of  a 
plant  dies,  and  remains  exposed  to  air  and  moisture  at  the 
common  temperatures,  it  undergoes  a  series  of  chemical 
and  physical  changes,  which  are  largely  due  to  an  oxida- 
tion of  portions  of  its  carbon  and  hydrogen,  and  the 
formation  of  new  organic  compounds.  Vegetable  matter 
is  considerably  variable  in  composition,  but  in  all  cases 
chiefly  consists  of  cellulose  and  starch,  or  bodies  of  simi- 
lar character,  mixed  witb  a  small  proportion  of  albuminous 
and  mineral  substances.  By  decay,  the  white  or  light- 
colored  and  tough,  tissues  of  plants  become  converted  into 
brown  or  black  friable  substances,  in  which  less  or  none 
of  the  organized  structure  of  the  fresh  plant  can  be 
traced.  The  bulk  and  weight  of  the  decaying  matter 
constantly  decreases  as  the  process  continues.  With  full 
access  of  air  and  at  suitable  temperatures,  the  decay, 
which,  from  the  first,  is  characterized  by  the  production 
and  escape  of  carbonic  acid  and  water,  proceeds  without 
interruption,  though  more  and  more  slowly,  until  nearly 
all  the  carbon  and  hydrogen  of  the  vegetable  matters  are 
oxidized  to  the  above-named  products,  and  little  more 
than  the  ashes  of  the  plant  remains.  With  limited  access 
of  air  the  process  rapidly  runs  through  a  first  stage  of 
oxidation,  when  it  becomes  checked  by  the  formation  of 
substances  which  are  tbemselves  able,  to  a  good  degree, 
to  resist  further  oxidation,  especially  under  the  circum- 
stances of  their  formation,  and  hence  they  accumulate  in 
considerable  quantities.  This  happens  in  the  lower  layers 
of  fallen  leaves  in  a  dense  forest,  in  compost  and  manure 
beaps,  in  the  sod  of  a  meadow  or  pasture,  and  especially 
in  swamps  and  peat-bogs. 

The  more  delicate,  porous  and  watery  the  vegetable 


138  HOW    CROPS    FEED. 

matter,  and  the  more  soluble  substances  and  albuminoids 
it  contains,  the  more  rapidly  does  it  decay  or  humify. 

It  has  been  shown  by  a  chemical  examination  of  what 
escapes  in  the  form  of  gas,  as  well  as  of  what  remains  as 
humus,  that  the  carbon  of  wood  oxidizes  more  slowly 
than  its  hydrogen,  so  that  humus  is  relatively  richer  in 
carbon  than  the  vegetable  matters  from  which  it  origin- 
ates. With  imperfect  access  of  air,  carbon  and  hydrogen 
are  to  some  extent  disengaged  in  union  with  each  other, 
as  marsh  gas  (CHJ.  Carbonic  oxide  gas  (CO)  is  proba- 
bly also  produced  in  minute  quantity.  The  nitrogen  of 
the  vegetable  matter  is  to  a  considerable  extent  liberated 
in  the  free  gaseous  state  ;  a  portion  of  it  unites  to  hydro- 
gen, forming  ammonia  (NH3),  which  remains  in  the  de- 
caying mass  ;  still  another  portion  remains  in  the  humus 
in  combination,  not  as  ammonia,  but  as  an  ingredient  of 
the  ill-defined  acid  bodies  v/hich  constitute  the  bulk  of 
humus ;  finally,  some  of  the  nitrogen  may  be  oxidized  to 
nitric  acid. 

Chemical  Nature  @f  Humus* — In  a  subsequent  chapter, 
(p.  224,)  the  composition  of  humus  will  be  explained  at 
length.  Here  we  may  simply  mention  that,  under  the  in- 
fluence of  alkalies  and  ammonia,  it  yields  one  or  more 
bodies  having  acid  characters,  called  humic  and  ulmic 
(also  geic)  acids.  Further,  by  oxidation  it  gives  rise  to 
crenic  and  apocrenic  acids.  The  former  are  faintly  acid 
in  their  properties ;  the  latter  are  more  distinctly  char- 
acterized acids. 

lafluesce  of  Humus  oa  tM  Minerals  of  tlie  Soil. — 
a.  Disintegration  of  the  mineral  matters  of  soils  is  aided 
by  the  presence  of  organic  substances  in  a  decaying  state,  in 
so  far  as  the  latter,  from  their  hygroscopic  quality,  main- 
tain the  surface  of  the  soil  in  a  constant  state  of  moisture. 
h.  Organic  matters  furnish  copious  supplies  of  carbonic 
acid^  the  action  of  which  has  already  been  considered 


OKIGIX    AND    FOKMATIOI^    OF    SOILS.  139 

(p.  128).  Boussingault  and  Lewy  {Memoires  de  Ghimie 
Agricole,  etc.^p.  369,)  have  analyzed  the  air  contained  in 
the  pores  of  the  soil,  and,  as  was  to  be  anticipated,  found 
it  vastly  richer  in  carbonic  acid  than  the  ordinary  atmos- 
phere. 

The  following  table  exhibits  the  composition  of  the  air 
in  the  soil  compared  with  that  of  the  air  above  the  soil, 
as  observed  in  their  investigations. 

Carbonic  acid  in  10,000 
parts  of  air  (by  weight). 

Ordinary  atmosphere 6 

Air  from  sandy  subsoil  of  forest 38 

"      "      loamy      "      "    "  124 

"      "      surface-soil     "    "  130 

*'      "  "  "    vineyard 146 

"      "  "  "    old  asparagus  bed 122 

"      "  *'  "     "        "    newly  manured.  233 

"      "  "  "   pasture 270 

"      "  "  rich  in  humus 543 

"      "  "  newly  manured  sandy  field, 

during  dry  weather 333 

"      "  "  newly  manured  sandy  field, 

during  wet  weather 1413 

That  this  carbonic  acid  originates  in  large  part  by  oxi- 
dation of  organic  matters  is  strikingly  demonstrated  by 
the  increase  in  its  quantity,  resulting  from  the  application 
of  manure,  and  the  supervention  of  warm,  wet  weather. 
It  is  obvious  that  the  carbonic  acid  contained  in  the  air 
of  the  soil,  being  from  twenty  to  one  hundred  or  more 
times  more  abundant,  relatively,  than  in  the  common  at- 
mosphere, must  act  in  a  correspondingly  more  rapid  and 
energetic  manner  in  accomplishing  the  solution  and  disin- 
tegration of  mineral  matters. 

G.  The  organic  acids  of  the  humus  group  probably  aid 
in  the  disintegration  of  soil  by  direct  action,  though  our 
knowledge  is  too  imperfect  to  warrant  a  positive  conclu- 
sion. The  ulmic  and  humic  acids  themselves,  indeed,  do 
not,  according  to  Mulder,  exist  in  the  free  state  in  the 
soil,  but  their  soluble  salts  of  ammonia,  potash  or  soda, 
have  acid  characters,  in  so  far  that  they  unite  energetical- 


140  now    CROPS    FEED. 

ly  with  other  bases,  as  lime,  oxide  of  iron,  etc.  These 
alkali-salts,  then,  should  attack  the  minerals  of  the  soil  in 
a  manner  similar  to  carbonic  acid.  The  same  is  probably 
true  of  crenic  and  apocrenic  acids. 

d.  It  scarcely  requires  mention  that  the  ammonia  salts 
and  nitrates  yielded  by  the  decay  of  plants,  as  well  as  the 
organic  acids,  oxalic,  tartaric,  etc.,  or  acid-salts,  and  the 
chlorides,  sulphates,  and  phosphates  they  contain,  act  upon 
the  surface  soil  where  they  accumulate  in  the  manner  al- 
ready described,  and  that  vegetable  (and  animal)  remains 
thus  indirectly  hasten  the  solution  of  mineral  matters. 

Action  ©f  Living  Plants  on  tlie  Minerals  of  the  Soil. — 

1.  Moisture  and  Carbonic  Acid. — The  living  vegetation 
of  a  forest  or  prairie  is  the  means  of  perpetually  bringing 
the  most  vigorous  disintegrating  agencies  to  bear  upon 
the  soil  that  sustains  it.  The  shelter  of  the  growing 
l^lants,  not  less  than  the  hygroscopic  humus  left  by  their 
decay,  maintains  the  surface  in  a  state  of  saturation  by 
moisture.  The  carbonic  acid  produced  in  living  roots, 
and  to  some  extent,  at  least,  it  is  certain,  excreted  from 
them,  adds  its  effect  to  that  derived  from  other  sources. 

2.  Organic  Acids  within  the  Plant. — According  to 
Zoller,  (  Ys.  jSt.  Y.  45)  the  young  roots  of  living  plants 
(what  plants,  is  not  mentioned)  contain  an  acid  or  acid- 
salt  which  so  impregnates  the  tissues  as  to  manifest  a 
strong  acid  reaction  with  (give  a  red  color  to)  blue  litmus- 
paper,  which  is  permanent,  and  therefore  not  due  to  car- 
bonic acid.  This  acidity,  Zoller  informs  us,  is  most  in- 
tense in  the  finest  fibrils,  and  is  exhibited  when  the  roots 
are  simply  wrapped  in  the  litmus-paper,  without  being  at 
all  (?)  crushed  or  broken.  The  acid,  whatever  it  may  be, 
thus  existing  within  the  roots  is  absorbed  by  p'orous  paper 
placed  externally  to  them. 

Previous  to  these  observations  of  Zoller,  Salm  Horst- 
mar  {Jour.fllr.  Praht.  Chem.  XL.  304,)  having  found  in  the 
ashes  of  ground  pine  {Lycopodium  com^planatum) ,  38°  1^  of 


ORIGIN   AND    FOSMATION    OF    SOILS.  141 

alumina,  while  in  the  ashes  of  juniper,  growing  beside 
the  Lycopodium,  this  substance  was  absent,  examined 
the  rootlets  of  both  plants,  and  found  that  the  former  had 
an  acid  reaction,  while  the  latter  did  not  affect  litmus- 
paper.  Salm  Horstraar  supposed  that  the  alumina  of 
the  soil  finds  its  way  into  the  Lycopodium  by  means  of 
this  acid.  Ritthausen  has  shown  that  the  Lycopodium 
contains  malic  acid,  and  since  all  the  alumina  of  the  plant ' 
may  be  extracted  by  water,  it  is  probable  that  the  acid 
reaction  of  the  rootlets  is  due,  in  part  at  least,  to  the 
presence  of  acid  malate  of  alumina.  {Jour.  far.  PraJct. 
Chem.  1111.  420.) 

At  Liebig's  suggestion,  Zoller  made  the  following  ex- 
periments. A  number  of  glass  tubes  were  filled  with 
water  made  slightly  acid  by  some  drops  of  hydrochloric 
acid,  vinegar,  citric  acid,  bitartrate  of  potash,  etc.  ;  the 
open  end  of  each  tube  was  then  closed  by  a  piece  of 
moistened  bladder  tied  tightly  over,  and  various  salts,  in- 
soluble in  water,  as  phosphate  of  lime,  phosphate  of  am- 
monia and  magnesia,  etc.,  were  strewn  on  the  bladder. 
After  a  short  time  it  was  found  that  the  ingredients  of 
these  salts  were  contained  in  the  liquid  in  contact  with 
the  under  surface  of  the  bladder,  having  been  dissolved 
by  the  dilute  acid  j^resent  in  the  pores  of  the  membrane, 
and  absorbed  through  it.  This  is  an  ingenious  illustra- 
tion of  the  mode  in  which  the  organic  acids  existing  in 
the  root-cells  of  plants  may  act  directly  upon  the  rock  or 
soil  external  to  them.  By  such  action  is  doubtless  to  be 
explained  the  fact  mentioned  by  Liebig  in  the  following 
words : 

"We  frequently  find  in  meadows  smooth  limestones 
with  their  surfaces  covered  with  a  network  of  small  fur- 
rows. When  these  stones  are  newly  taken  out  of  the 
ground,  we  find  that  each  furrow  corresponds  to  a  rootlet, 
which  appears  as  if  it  had  eaten  its  way  into  the  stone." 
{Modern  Ag.  p.  43.) 


142  HOW    CROPS    FEED. 

This  direct  action  of  the  living  j^lant  is  probably  ex- 
erted by  the  lichens,  which,  as  has  been  already  stated, 
grow  npon  the  smooth  surface  of  the  rock  itself.  Many 
of  the  lichens  are  known  to  contain  oxalate  of  lime  to  the 
extent  of  half  their  weight  (Braconnot). 

According  to  Goeppert,  the  hard,  fine-grained  rock  of  the 
Zobtenberg,  a  mountain  of  Silesia,  is  in  all  cases  softened  at 
its  surface  where  covered  with  lichens  {Acarospora  smar- 
agdula,  Imhricaria  oUvacea,  etc.),  while  the  bare  rock, 
closely  adjacent,  is  so  hard  as  to  resist  the  knife.  On  the 
Schwalbenstein,  near  Glatz,  in  Silesia,  at  a  height  of  4,500 
feet,  the  granite  is  disintegrated  under  a  covering  of  li- 
chens, the  feldspar  being  converted  into  kaolin  or  washed 
away,  only  the  grains  of  quartz  and  mica  remaining  unal- 
tered.* 


CHAPTER    III. 

KINDS  OF  SOILS— THEIR  DEFINITION  AND   CLASSIFI- 
CATION. 


DISTINCTION  OF  SOILS   BASED  UPON   THE   MODE  OF  THEIR 
FORMATION  OR  DEPOSITION. 

The  foregoing  considerations  of  the  origin  of  soils  intro- 
duce us  appropriately  to  the  study  of  soils  themselves. 
In  the  next  place  we  may  profitably  recount  those  defini- 
tions and  distinctions  that  serve  to  give  a  certain  degree 
of  precision  to  language,  and  enable  us  to  discriminate  in 
some  measure  the  diff*erent  kinds  of  soils,  which  ofier 
great  diversity  in  origin,  composition,  external  characters, 


See,  also,  p.  136. 


KIXDS    OF    SOILS.  143 

and  fertility.  Unfortunately,  while  there  are  almost  num- 
berless varieties  of  soil  having  numberless  grades  of  pro- 
ductive power,  we  are  very  deficient  in  terms  by  which  to 
express  concisely  even  the  fact  of  their  differences,  not  to 
mention  our  inability  to  define  these  differences  with  ac- 
curacy, or  our  ignorance  of  the  precise  nature  of  their 
jDeculiarities. 

As  regards  mode  of  formation  or  deposition,  soils  are 
distinguished  into  Sedentary  and  Transported.  Tlie  lat- 
ter are  subdivided  into  Drifts  Alluvial^  and  CoUumal 
soils. 

Sedentary  SoilS^  or  Soils  in  place.,  are  those  which  have 
not  been  transported  by  geological  agencies,  but  which 
remain  where  they  were  formed,  covering  or  contiguous 
to  the  rock  from  whose  disintegration  they  originated. 
Sedentary  soils  have  usually  little  depth.  An  inspection 
of  the  rock  underlying  such  soils  often  furnishes  most 
valuable  information  regarding  their  composition  and 
probable  agricultural  value ;  because  the  still  unweathered 
rock  reveals  to  the  practised  eye  the  nature  of  the  min- 
erals, and  thus  of  the  elements,  composing  it,  while  in  the 
soil  these  may  be  indistinguishable. 

In  ]N"ew  England  and  the  region  lying  north  of  the  Ohio 
and  east  of  the  Missouri  rivers,  soils  iu  place  are  not 
abundant  as  compared  with  the  entire  area.  Nevertheless 
they  do  occur  in  many  small  patches.  Thus  the  red-sand- 
stone of  the  Connecticut  Yalley  often  crops  out  in  that 
part  of  ]!!^ew  England,  and,  being,  in  many  localities,  of  a 
friable  nature,  has  crumbled  to  soil,  which  now  lies  undis- 
turbed in  its  original  position.  So,  too,  at  the  base  of  trap- 
bluffs  may  be  found  trap-soils,  still  full  of  sharp-angled 
fragments  of  the  rock. 

Transported  Soils,  (subdivided  into  drift,  alluvial,  and 
colluvial),  are  those  which  have  been  removed  to  a  dis- 
tance from  the  rock-beds  whence  they  originated,  by  the 


144  HOW    CROPS    FEED. 

action  of  moving  ice  (glaciers)  or  water  (rivers),  and  de- 
posited as  sediment  in  their  present  positions. 

Drift  Soils  (sometimes  called  diluvial)  are  cliaracterized 
by  the  following  particulars.  They  consist  of  fragments 
whose  edges  at  least  have  been  rounded  by  friction,  if  the 
iragments  themselves  are  not  altogether  destitute  of 
angles.  They  are  usually  deposited  without  any  stratifi- 
cation or  separation  of  parts.  The  materials  consist  of 
soil  proper,  mingled  with  stones  of  all  sizes,  from  sand- 
grains  up  to  immense  rock-masses  of  many  tons  in  weight. 
This  kind  of  soil  is  usually  distinguished  from  all  others 
by  the  rounded  rocks  or  boulders  ("  hard  heads  ")  it  con- 
tains, which  are  promiscuously  scattered  through  it. 

The  "Drift"  has  imdoubtedly  been  formed  by  moving 
ice  in  that  period  of  the  earth's  history  known  to  geolo- 
gists as  the  Glacial  Epoch,  a  period  when  the  present  sur- 
face of  the  country  was  covered  to  a  great  depth  by  fields 
of  ice. 

In  regions  like  Greenland  and  the  Swiss  Alps,  which 
reach  above  the  line  of  perpetual  snow,  drift  is  now  ac- 
cumulating, perfectly  similar  in  character  to  that  of  N'ev/ 
England,  or  has  been  obviously  produced  by  the  melting 
of  glaciers,  which,  in  former  geological  ages  and  under 
a  colder  climate,  were  continuations  on  an  immense  scale 
of  those  now  in  existence. 

A  large  share  of  the  northern  portion  of- the  country 
from  the  Arctic  regions  southward  as  far  as  latitude  39°, 
or  nearly  to  the  southern  boundaries  of  Pennsylvania  and 
to  the  Ohio  Kiver,  including  Canada,  N'ew  England,  Long 
Island,  and  the  States  v/est  as  far  as  Iowa,  is  more  or  less 
covered  with  drift.  Comparison  of  the  boulders  with  the 
undisturbed  rocks  of  the  regions  about  show  that  the 
materials  of  the  drift  have  been  moved  southwards  or 
southeastwards  to  a  distance  generally  of  twenty  to  forty 
miles,  but  sometimes  also  of  sixty  or  one  hundred  miles, 
from  where  they  were  detached  from  their  original  beds. 


KINDS    OF    SOILS.  145 

The  surface  of  the  country  when  covered  with  drift  is 
often  or  usually  irregular  and  hilly,  the  hills  themselves 
being  conical  heaps  or  long  ridges  of  mingled  sand,  gravel, 
and  boulders,  the  transported  mass  having  often  a  great 
depth.  These  hills  or  ridges  are  parts  of  the  vast  trains 
of  material  left  by  the  melting  of  preadamite  glaciers  or 
icebergs,  and  have  their  precise  counterpart  in  the  'inoraines 
of  the  Swiss  Alps.  Drift  is  accordingly  not  confined  to  the 
valleys,  but  the  northern  slopes  of  mountains  or  hills,  whose 
basis  is  unbroken  rock,  are  strewn  to  the  summit  with  it, 
and  immense  blocks  of  transported  stone  are  seen  upon 
the  very  tops  of  the  Catskills  and  of  the  White  and 
Green  Mountains. 

Drift  soils  are  for  these  reasons  often  made  up  of  the 
most  diverse  materials,  including  all  the  kinds  of  rock  and 
rock-dust  that  are  to  be  found,  or  have  existed  for  one  or 
several  scores  of  miles  to  the  northward.  Of  these  often 
only  the  harder  granitic  or  silicious  rocks  remain  in  con- 
siderable fragments,  the  softer  rocks  having  been  com- 
pletely ground  to  pov/der. 

Towards  the  southern  limit  of  the  Drift  Region  the 
drift  itself  consists  of  fine  materials  which  were  carried 
on  by  the  waters  from  the  melting  glaciers,  Avhile  the 
heavier  boulders  were  left  further  north.  Here,  too,  may 
ofteix  be  observed  a  partial  stratification  of  the  transported 
materials  as  the  result  of  their  deposition  from  moving 
water.  The  great  belts  of  yellow  and  red  sand  that 
stretch  across  jSTew  Jersey  on  its  southeastern  face,  and 
the  sands  of  Long  Island,  are  these  finer  portions  of  the 
drift.  Farther  to  the  north,  many  large  areas  of  sand 
may,  perhaps,  prove  on  careful  examination  to  mark  the 
southern  limit  of  some  ancient  local  glacier. 

Alluvial  Soils  consist  of  worn  and  roimded  materials 
which  have  been  transported  by  the  agency  of  running 
water  (rivers  and  tides).  Since  small  and  light  particles 
are  more  readilv  sustained  in  a  current  of  water  than 


146  HOW    CROPS    FEED. 

heavy  masses,  alluvium  is  always  more  or  less  stratified 
or  arranged  in  distinct  layers :  stones  or  gravel  at  the 
bottom  and  nearest  the  source  of  movement,  finer  stones 
or  finer  gravel  above  and  further  down  in  the  path  of 
flow,  sand  and  impalpable  matters  at  the  surface  and  at 
the  point  where  the  stream,  before  turbid  from  suspended 
rock-dust,  finally  clears  itself  by  a  broad  level  course  and 
slow  progress. 

Alluvial  deposits  have  been  formed  in  all  periods  of  the 
earth's  history.  Water  trickling  gently  down  a  granite 
slope  carries  forward  the  kaolinite  arising  from  decompo- 
sition of  feldspar,  and  the  first  hollow  gradually  fills  up 
with  a  bed  of  clay.  In  valleys  are  thus  deposited  the 
gravel,  sand,  and  rock-dust  detached  from  the  slopes  of 
neighboring  mountains.  Lakes  and  gulfs  become  filled 
with  silt  brought  into  them  by  streams.  Alluvium  is 
found  below  as  well  as  above  the  drift,  and  recent  alluvium 
in  the  drift  region  is  very  often  composed  of  drift  mate- 
rials rearranged  by  water-currents.  Alluvium  often  con- 
tains rounded  fragments  or  disks  of  soft  rocks,  as  lime- 
stones and  slates,  which  are  more  rarely  found  in  drift. 

Colluvial  Soils,  lastly,  are  those  which,  while  consisting 
in  23att  of  drift  or  alluvium,  also  contain  sharp,  angular 
fragments  of  the  rock  from  which  they  mainly  originated, 
thus  demonstrating  that  they  have  not  been  transported 
to  any  great  distance,  or  are  made  up  of  soils  in  place, 
more  or  less  mingled  with  drift  or  alluvium. 

§s. 

DISTINCTIONS  OF  SOILS   BASED    UPON  OBVIOUS  OR  EXTER- 
NAL  CHARACTERS. 

The  classification  and  nomenclature  of  soils  customarily 
employed  by  agriculturists  have  chiefly  arisen  from  con- 
sideration of  the  relative  proportions  of  the  principal 


KINDS    OF    SOILS.  147 

meclianical  ingredients,  or  from  other  highly  obvious 
qualities. 

The  distinctions  thus  established,  though  very  vague 
scientifically  considered,  are  extremely  useful  for  practical 
purposes,  and  the  grounds  upoQ  which  they  rest  deserve 
to  be  carefully  reviewed  for  the  purpose  of  appreciating 
their  deficiencies  and  giving  greater  precision  to  the  terms 
employed  to  define  them. 

The  farmer,  speaking  of  soils,  defines  them  as  cp^avelly^ 
sandy ^  clayey^  loamy ^  calcareous^  peaty ^  ochreous,  etc. 

Mechaniccil  Analysis  of  the  Soil. — Before  noticing 
these  various  distinctions  in  detail,  we  may  appropriately 
study  the  methods  which  are  employed  for  separating  the 
mechanical  ingredients  of  a  soil.  It  is  evident  that  the 
epithet  sandy ^  for  example,  should  not  be  applied  to  a  soil 
unless  sand  be  the  predominating  ingredient ;  and  in  or- 
der to  apply  the  term  with  strict  correctness,  as  well  as  to 
know  how  a  soil  is  constituted  as  regards  its  mechanical 
elements,  it  is  necessary  to  isolate  its  parts  and  determine 
their  relative  quantity. 

Boulders,  stones,  and  pebbles,  are  of  little  present  or 
immediate  value  in  the  soil  by  way  of  feeding  the  plant. 
This  function  is  performed  by  the  finer  and  especially  by 
the  finest  particles.  Mechanical  analysis  serves  therefore 
to  compare  together  difierent  soils,  and  to  give  useful  in- 
dications of  fertility.  Simple  inspection  aided  by  the  feel 
enables  one  to  judge,  perhaps,  with  sufilcient  accuracy  for 
all  ordinary  practical  purposes ;  but  in  any  serious  attempt 
to  define  a  soil  precisely,  for  the  purposes  of  science,  its 
mechanical  analysis  must  be  made  with  care. 

Mechanical  separation  is  effected  by  sifting  and  wash- 
ing. Sifting  serves  only  to  remove  the  stones  and  coarse 
sand.  By  placing  the  soil  in  a  glass  cylinder,  adding  wa- 
ter, and  vigorously  agitating  for  a  few  moments,  then 
letting  the  whole  come  to  rest,  there  remains  suspended 
in  the  water  a  greater  or  less  quantity  of  matter  in  a  state 


148  HOW    CHOPS    FEED. 

of  extreme  division.  This  fine  matter  is  in  many  cases 
clay  (kaolinite),  or  at  least  consists  of  substances  resulting 
from  the  weathering  of  the  rocks,  and  is  not,  or  not  chiefly, 
rock-dust.  Between  this  impalpably  fine  matter  and  the 
grains  of  sand  retained  by  a  sieve,  there  exist  numberless 
gradations  of  fineness  in  the  particles. 

By  conducting  a  slow  stream  of  water  through  a  tube 
to  the  bottom  of  a  vessel,  the  fine  particles  of  soil  are 
carried  off  and  may  be  received  in  a  pan  j^laced  beneath. 
Increasing  the  rapidity  of  the  current  enables  it  to  remove 
larger  particles,  and  thus  it  is  easy  to  separate  the  soil  in- 
to a  number  of  portions,  each  of  which  contains  soil  of  a 
different  fineness. 

Various  attempts  have  been  made  to  devise  precise 
means  of  separating  the  materials  of  soils  mechanically 
into  a  definite  number  of  grades  of  fineness. 

This  may  be  accomplished  in  good  measure  by  Vv^asliing, 
but  constant  and  accurate  results  are  of  course  only  at- 
tained when  the  circumstances  of  the  washing  are  uniform 
throughout.  The  method  adopted  by  the  Society  of 
Agricultural  Chemists  of  Germany  is  essentially  the  fol- 
lowing (  Yersuchs  Stationen^  VI,  144) : 

The  air-dry  soil  is  gently  rubbed  on  a  tin-plate  sieve 
with  round  holes  three  millimeters  in  diameter ;  what  passes 
is  weighed  as  fine-earth.  What  remains  on  the  sieve  is 
washed  v\^ith  water,  dried,  weighed,  and  designated  as 
gravel,  pebbles,  stones,  as  the  case  may  be,  the  size  of  the 
stones,  etc.,  being  indicated  by  comparison  with  the  fist, 
witb  an  (i%%^  a  walnut,  a  hazelnut,  a  pea,  etc.  Of  \hQ  fine- 
earth  a  portion  (30  grams)  is  now  boiled  for  an  hour  or  more 
in  water,  so  as  to  completely  break  down  any  lumps  and 
separate  adhering  particles,  and  is  then  left  at  rest  for 
some  minutes,  when  it  is  transferred  into  the  vessel  1  of 
the  apparatus,  fig.  8.,  after  having  poured  off  the  turbid 
water  with  which  it  vv^as  boiled,  into  2t  This  washing  ap- 
paratus (invented  by  Nobel)  consists  of  a  reservoir,  A^ 


KINDS    OF    SOILS. 


149 


made  of  sheet  metal,  capable  of  holding  something  more 
than  9  liters  of  water,  and  furnished  at  h  with  a  stop-cock. 
By  means  of  a  tube  of  rubber  it  is  joined  to  the  series  of 


Fig.  8. 


vessels,  1,  2,  S,  and  4,  which  are  connected  to  each  other, 
as  shown  in  the  figure,  the  recurved  neck  of  2  fitting 
water-tight  into  the  nozzle  of  1  at  a,  etc. 

These  vessels  are  made  of  glass,  and  together  hold  4 
liters  of  vf ater ;  their  relative  volume  is  nearly 

1  :  8  :  27  :  64,  or  =  1=^  :  2^  S^-  :  4\ 

5  is  a  glass  vessel  of  somewhat  more  than  5  liters, 
capacity. 

The  distance  between  h  and  c  is  2  feet.  The  cock,  5,  is 
opened,  so  that  in  20  minutes  exactly  9  liters  of  water 


150  HOW    CEOPS    FEED. 

pass  it.  Tbe  apparatus  being  joined  together,  and  the 
cock  opened,  the  soil  in  1  is  agitated  by  tbe  stream  of  wa- 
ter flowing  through,  and  the  finer  portions  are  carried  over 
into  2 J  3}  4 J  and  5»  As  a  given  amount  of  water  requires 
eight  times  longer  to  pass  through  2  than  1,  its  velocity 
of  motion  and  buoyant  power  in  the  neck  of  3  are  corre- 
spondingly less.  After  the  requisite  amount  of  water  has 
run  from  A,  the  cock  is  closed,  the  whole  left  to  rest  sev- 
eral hours,  when  the  contents  of  the  vessels  are  separately 
rinsed  out  into  porcelain  dishes,  dried  and  weighed.* 

The  contents  of  the  several  vessels  are  designated  as 
follows  :f 

1.  Gravel,  fragments  of  rock. 

2.  Coarse  sand. 

3.  Fine  sand. 

4.  Finest  or  dust  sand. 

5.  Clayey  substance  or  impalpable  matter. 

In  most  inferior  soils  the  gravel,  the  coarse  sand,  and 
the  fine  sand,  are  angular  fragments  of  quartz,  feldspar, 
amphibole,  pyroxene,  and  mica,  or  of  rocks  consisting  of 
these  minerals.  It  is  only  these  harder  and  less  easily 
decomposable  minerals  that  can  resist  the  pulverizing 
agencies  through  which  a  large  share  of  our  soils  have 
passed.  In  the  more  fertile  soils,  formed  from  sedimen- 
tary limestones  and  slates,  the  fragments  of  these  strati- 
fied rocks  occur  as  flat  pebbles  and  rounded  grains. 

The  finest  or  dust-sand,  when  viewed  under  the  micro- 
scope, is  found  to  be  the  same  rocks  in  a  higher  state  of 
pulverization. 


*  See,  also,  Wolff's  '■'■  Anieitung  zur  UntersuchunglandivirthscJiaftlich-wichUger 
JStqfe,''  1867,  p.  5. 

t  These  names,  applied  by  Wolff  to  the  results  of  washing  the  sedentary  soils 
of  Wiirtemberg,  do  not  always  well  apply  to  other  soils.  Thus  Grouven,  (3to'  Salz- 
niunder  Bericht,  p.  32),  operating  on  the  alluvial  soils  of  North  Gennauy,  desig- 
nated the  contents  of  the  4th  funnel  as  "clay  and  loam,"  and  those  of  the  5th 
vessel  as  "  light  clay  and  humus."  Again,  Schone  found  {Bulletin,  etc.,  de  Moscou, 
p.  402)  by  treatment  of  a  certain  soil  in  Nobel's  apparatus,  45  per  cent  of  "  coarse 
sand  "  remaining  in  the  2d  funnel.  The  particles  of  this  were  for  the  most  part 
smaller  than  l-lOtb  millimeter  (l-SaOth  inch),  which  certainly  is  not  coarse  sand  t 


KINDS    OF    SOILS.  151 

What  is  designated  as  clayey  substance^  or  impalpable 
matter^  is  oftentimes  largely  made  up  of  rock-dust,  so  fine 
that  it  is  supported  by  water,  Avhen  the  latter  is  in  the 
gentlest  motion.  In  what  are  properly  termed  clay-soils, 
the  finest  parts  consist,  however,  chiefly  of  the  hydrous 
silicate  of  alumina,  already  described,  p.  113,  under  the 
mineralogical  name  of  kaolinite^  or  of  analogous  com- 
pounds, mixed  with  gelatinous  silica,  oxides  of  iron,  and 
carbonate  of  lime,  as  well  as  with  finely  divided  quartz 
and  other  granitic  minerals.  So  gradual  is  the  transition 
from  true  kaolinite  clay  through  its  impurer  sorts  to  mere 
impalpable  rock-dust,  in  all  that  relates  to  sensible  char- 
acters, as  color,  feel,  adhesiveness,  and  plasticity,  that  the 
term  clay  is  employed  rather  loosely  in  agriculture,  being 
not  infrequently  given  to  soils  that  contain  very  little 
kaolinite  or  true  clay,  and  thus  implies  the  general  physi- 
cal qualities  that  are  usually  typified  by  clay  rather  than 
the  presence  of  any  definite  chemical  compound,  like 
kaolinite,  in  the  soil. 

Many  soils  contain  much  carbonate  of  lime  in  an  im- 
palpable form,  this  substance  having  been  derived  from 
lime  rocks,  as  marble  and  chalk,  from  the  shells  of  mollusks, 
or  from  coral ;  or  from  clays  that  have  originated  by  the 
chemical  decomposition  of  feldspathic  rocks  containing 
much  lime. 

Organic  matter^  especially  the  debris  of  former  vegeta- 
tion, is  almost  never  absent  from  the  imj)alpable  portion 
of  the  soil,  existing  there  in  some  of  the  various  forms  as- 
sumed by  humus. 

As  Schone  has  shown,  {Bulletin  de  la  Societe  des  JSTatura- 
listes  de  Moscou,  1867,  p.  363),  the  results  obtained  by 
Nobel's  apparatus  are  far  from  answering  the  purposes  of 
science.  The  separation  is  not  carried  far  enough,  and  no 
simple  relations  subsist  between  the  separated  portions,  as 
regards  the  dimensions  of  their  particles.  If  the  soil  were 
composed  of  spherical  particles  of  one  kind  of  matter,  or 


152  KOW    CROPS    FEED. 

having  all  the  same  specific  gravity,  it  would  be  possible 
by  the  use  of  a  properly  constructed  washing  apparatus 
to  separate  a  sample  into  fifty  or  one  hundred  parts,  and 
to  define  the  dimensions  of  the  particles  of  each  of  these 
parts.  Since,  however,  the  soil  is  very  heterogeneous,  and 
since  its  particles  are  unlike  in  shape,  consisting  partly  of 
nearly  spherical  grains  and  partly  of  plates  or  scales  upon 
which  moving  water  exerts  an  unequal  floating  effect,  it  is 
difficult,  if  not  impossible,  to  realize  so  perfect  a  mechanic- 
al analysis.  It  is,  however,  easy  to  make  a  separation  of  a 
soil  into  a  large  number  of  parts,  each  of  which  shall  ad- 
mit of  precise  definition  in  terms  of  the  rapidity  of  flow 
of  a  current  of  water  capable  of  sustaining  the  particles 
which  compose  it.  Instruments  for  mechanical  analysis, 
which  provide  for  producing  and  maintaining  at  will  any 
desired  rate  of  flow  in  a  stream  of  water,  have  been  very 
recently  devised,  independently  of  each  other,  by  E.  Schone 
{loG.  cit,  pp.  334-405)  and  A.  Muller  {Vs.  St.,  X,  25-51). 
The  employment  of  such  apparatus  promises  valuable  re- 
sults, although  as  yet  no  extended  investigations  made 
with  its  help  have  been  published. 

Crravelly  Soils  are  so  named  from  the  abundance  of 
small  stones  or  pebbles  in  them.  This  name  alone  gives 
but  little  idea  of  the  really  important  characters  of  the 
soil.  Simple  gravel  is  nearly  valueless  for  agricultural 
purposes ;  many  highly  gravelly  soils  are,  however,  very 
fertile.  The  fine  portion  of  the  soil  gives  them  their  crop- 
feeding  power.  The  coarse  parts  ensure  drainage  and 
store  the  solar  heat.  The  mineralogical  characters  of  the 
pebbles  in  a  soil,  as  determined  by  a  practised  eye,  may 
often  give  useful  indications  of  its  composition,  since  it 
is  generally  true  that  the  finer  parts  of  the  soil  agree  in 
this  respect  with  the  coarser,  or,  if  dififerent,  are  not  in- 
ferior. Thus  if  the  gravel  of  a  soil  contains  many  pebbles 
of  feldspar,  the  soil  itself  may  be  concluded  to  be  well 
supplied  with  alkalies ;  if  the  gravel  consists  of  limestone, 


KINDS    OF    SOILS.  153 

we  may  infer  that  lime  is  abundant  in  the  soil.  On  the 
otlier  hand,  if  a  soil  contains  a  large  proportion  of  quartz 
pebbles,  the  legitimate  inference  is  that  it  is  of  compara- 
tively poor  quality.  The  term  gravelly  admits  of  various 
qualification.  We  may  have  a  very  gravelly  or  a  mod- 
erately gravelly  soil,  and  the  coarse  material  may  be  char- 
acterized as  a  fine  or  coarse  gravel,  a  slaty  gravel,  a 
granitic  gravel,  or  a  diorite  gravel,  according  to  its  state 
of  division  or  the  character  of  the  rock  from  which  it  was 
formed. 

But  the  closest  description  that  can  thus  be  given  of  a 
gravelly  soil  cannot  convey  a  very  precise  notion  of  even 
its  external  qualities,  much  less  of  those  properties  upon 
which  its  fertility  depends. 

Sandy  Soils  are  those  which  visibly  consist  to  a  large 
degree,  90°  |g  or  more,  of  sand,  i.  e.,  of  small  granular 
fragments  of  rock,  no  matter  of  what  kind.  Sand  usually 
signifies  grains  of  quartz;  this  mineral,  from  its  hardness, 
withstanding  the  action  of  disintegrating  agencies  beyond 
any  other.  Considerable  tracts  of  nearly  pure  and  white 
quartz  sand  are  not  uncommon,  and  are  characterized  by 
obdurate  barrenness.  But  in  general,  sandy  soils  are  by  no 
means  free  from  other  silicious  minerals,  especially  feldspar 
and  mica.  When  the  sand  is  yellow  or  red  in  color,  this  fact 
is  due  to  admixture  of  oxide  or  silicates  of  iron,  and  points 
with  certainty  to  the  presence  of  ferruginous  minerals  or 
their  decomposition-products,  which  often  give  considera- 
ble fertility  to  the  soil. 

Other  varieties  of  sand  are  not  uncommon..  In  JSTew 
Jersey  occur  extensive  deposits  of  so-called  green  sand, 
containing  grains  of  a  mineral,  glauconite,  to  be  hereafter 
noticed  as  a  fertilizer.  Lime  sand,  consisting  of  grains 
of  carbonate  of  lime,  is  of  frequent  occurrence  on  the 
shores  of  coral  islands  or  reefs.  The  term  sandy-soil  is 
obviously  very  indefinite,  including  nearly  the  extremes 


154  HOW    CROPS    FEED. 

of  fertility  and  barrenness,  and  covering  a  wide  range  of 
variety  as  regards  composition.  It  is  therefore  qualified 
by  various  epithets,  as  coarse,  fine,  etc.  Coarse,  sandy 
soils  are  usually  unprofitable,  while  fine,  sandy  soils  are 
often  valuable. 

Clayey  Soils  are  those  in  which  clay  or  impalpable  mat- 
ters predominate.  They  are  commonly  characterized  by 
extreme  fineness  of  texture,  and  by  great  retentive  power 
for  water ;  this  liquid  finding  passage  through  their  pores 
with  extreme  slowness.  When  dried,  they  become  crack- 
ed and  rifted  in  every  direction  from  the  shrinking  that 
takes  place  in  this  process. 

It  should  be  distinctly  understood  that  a  soil  may  be 
clayey  without  being  clay,  i.  e.,  it  may  have  the  external, 
physical  properties  of  adhesiveness  and  impermeability  to 
water  which  usually  characterize  clay,  without  containing 
those  compounds  (kaolinite  and  the  like)  which  constitute 
clay  in  the  true  chemical  sense. 

On  the  other  hand  it  were  possible  to  have  a  soil  consist- 
ing chemically  of  clay,  which  should  have  the  physical 
properties  of  sand ;  for  kaolinite  has  been  found  in  crys- 
tals joVo  of  an  inch  in  breadth,  and  destitute  of  all  cohesive- 
ness  or  plasticity.  Kaolinite  in  such  a  coarse  form  is,  how- 
ever, extremely  rare,  and  not  likely  to  exist  in  the  soil. 

Loamy  Soils  are  those  intermediate  in  character  between 
sandy  and  clayey,  and  consist  of  mixtures  of  sand  with 
clay,  or  of  coarse  with  impalpable  matters.  They  are  free 
from  the  excessive  tenacity  of  clay,  as  well  as  from  the  too 
great  porosity  of  sand. 

The  gradations  between  sandy  and  clayey  soils  are 
roughly  expressed  by  such  terms  and  distinctions  as  the 
following : 


KINDS 

OF    SOILS. 

Clay 

or  impaIx)aLle  matters. 

Sand. 

Meavy  clay  contaius 

75— 90o|o 

10-  25' 

Clay  loam         " 

60—75 

25-40 

Loam                " 

40—60 

40—60 

Sandy  loam      " 

25—40 

60—  75 

Light  sandy  loam  contains 

10—25 

75—  90 

Sand                           ' 

0—10 

90-100 

155 


The  percentage  composition  above  given  applies  to 
the  dry  soil,  and  must  be  received  with  great  allowance, 
since  the  transition  from  fine  sand  to  impalpable  matter 
not  physically  distinguishable  from  clay,  is  an  impercep- 
tible one,  and  therefore  not  well  admitting  of  nice  discrim- 
ination. 

It  is  furthermore  not  to  be  doubted  that  the  difference 
between  a  clayey  soil  and  a  loamy  soil  depends  more  on 
the  form  and  intimacy  of  admixture  of  the  ingredients, 
than  upon  their  relative  proportions,  so  that  a  loam  may 
exist  which  contains  less  sand  than  some  clayey  soils. 

Calcareous  or  Lime  Soils  are  those  in  which  carbonate 
of  lime  is  a  predominating  or  characteristic  ingredient. 
They  are  recognizable  by  effervescing  vigorously  when 
drenched  with  an  acid.  Strong  vinegar  answers  for  test- 
ing them.  They  are  not  uncommon  in  Europe,  but  in  this 
country  are  comparatively  rare.  In  the  Northern  and 
Middle  States,  calcareous  soils  scarcely  occur  to  an  extent 
worthy  of  mention. 

While  lime  soils  exist  containing  75"  \^  and  more  of  car- 
bonate of  lime,  this  ingredient  is  in  general  subordinate 
to  sand  and  clay,  and  we  have  therefore  calcareous  sands, 
calcareous  clays,  or  calcareous  loams. 

Marls  are  mixtures  of  clay  or  clayey  matters,  >vith  finely 
divided  carbonate  of  lime,  in  something  like  equal  propor- 
tions.* 

Peat  or  Swamp  Muck  is  humus  resulting  from  decayed 


*  In  New  Jersey,  green  sand  marl.,  or  marl  simply,  is  the  name  applied  to  the 
green  sand  employed  as  a  fertilizer.  Shell  marl  is  a  name  designating  nearly 
pure  carbonate  of  lime  found  in  swamps. 


15G  HOW    CKOPS    FEED. 

vegetable  matter  in  bogs  and  marshes.  A  soil  is  peaty  or 
mucky  when  containing  vegetable  remains  that  have  suf- 
fered partial  decay  under  water. 

Vegetable  Mold  is  a  soil  containing  much  organic  mat- 
ter that  has  decayed  without  submergence  in  water,  either 
resulting  from  the  leaves,  etc.,  of  forest  trees,  from  the 
roots  of  grasses,  or  from  the  frequent  application  of  large 
doses  of  strawy  manures. 

Ocliery  or  FerrngiiiOllS  Soils  are  those  containing  much 
oxide  or  silicates  of  iron;  they  have  a  yellow,  red,  or 
broAvn  color. 

Other  divisioas  are  current  among  practical  men,  as, 
for  example,  surface  and  subsoil,  active  and  inert  soil, 
tilth,  and  hard  pan.  These  terms  mostly  explain  them- 
selves. When,  at  the  depth  of  four  inches  to  one  foot  or 
more,  the  soil  assumes  a  different  color  and  texture,  these 
distinctions  have  meaning. 

The  surface  soil^  active  soil,  or  tilth,  is  the  portion  that 
is  wrought  by  the  instruments  of  tillage — that  which  is 
moistened  by  the  rains,  warmed  by  the  sun,  permeated  by 
the  atmosphere,  in  which  the  plant  extends  its  roots,  gath- 
ers its  soil-food,  and  which,  by  the  decay  of  the  subter- 
ranean organs  of  vegetation,  acquires  a  content  of  humus. 

Subsoil. — Where  the  soil  originally  had  the  same  char- 
acters to  a  great  depth,  it  often  becomes  modified  down 
to  a  certain  point,  by  the  agencies  just  enumerated,  in 
such  a  manner  that  the  eye  at  once  makes  the  distinction 
into  surface  soil  and  subsoil.  In  many  cases,  however, 
such  distinctions  are  entirely  arbitrary,  the  earth  changing 
its  appearance  gradually  or  even  remaining  uniform  to  a 
considerable  depth.  Again,  the  surface  soil  may  have  a 
greater  downward  extent  than  the  active  soil,  or  the  tilth 
may  extend  into  the  subsoil. 

Hard  pan  is  the  appropriate  name  of  a  dense,  almost 
impenetrable,  crust  or  stratum  of  ochery   clay  or  com- 


PHYSICAL    CHAPwACTEES    OF    THE    SOIL.  157 

pacted  gravel,  often  underlying  a  fairly  fruitful  soil.  It 
is  the  soil  reverting  to  rock.  The  particles  once  disjointed 
are  being  cemented  together  again  by  the  solutions  of 
lime,  iron,  or  alkali-silicates  and  humates  that  descend  from 
the  surface  soil.  Such  a  stratum  often  separates  the  sur- 
face soil  from  a  deep  gravel  bed,  and  peat  swamps  thus 
exist  in  basins  formed  on  the  most  porous  soils  by  a  thin 
layer  of  moor-'bedj-pan. 

With  these  general  notions  regarding  the  origin  and 
characters  of  soils,  we  may  proceed  to  a  somewhat  extend- 
ed notice  of  the  properties  of  the  soil  as  influencing  fertil- 
ity. These  divide  themselves  into  physical  characters — 
those  which  externally  affect  the  growth  of  the  plant ; 
and  chemical  characters — those  which  provide  it  with  food. 


CHAPTER    IV. 

PHYSICAL    CHARACTERS    OF    THE    SOIL. 

The  physical  characters  of  the  soil  are  those  which  con- 
cern the  form  and  arrangement  of  its  visible  or  palpable 
particles,  and  likewise  include  the  relations  of  these  parti- 
cles to  each  other,  and  to  air  and  water,  as  well  as  to  the 
forces  of  heat  and  gravitation.  Of  these  physical  char- 
acters we  have  to  notice  : 

1.  The  Weight  of  Soils. 

2.  State  of  Division. 

3.  Absorbent  Power  for  Vapor  of  Water,  or  Hygro- 
scopic Capacity. 

4.  Property  of  Condensing  Gases. 

5.  Power  of  fixing  Solid  Matters  from  their  Solutions. 

6.  Permeability  to  Liquid  Water.     Capillary  Power. 

7.  Changes  of  Bulk  by  Drying,  etc. 

8.  Adhesiveness. 

9.  Relations  to  Heat. 


158  HOW    CROPS    FEED. 

In  treating  of  the  physical  characters  of  the  soil,  the 
writer  employs  an  essay  on  this  subject,  contributed  by 
him  to  Yol.  XVI  of  the  Transactions  of  the  iN".  Y.  State 
Agricultural  Society,  and  reproduced  in  altered  form  in  a 
Lecture  given  at  the  Smithsonian  Institution,  Dec,  1859. 

§1- 

THE  WEIGHT  OF  SOILS. 

The  Absolute  Weight  of  Soils  varies  directly  with  their 
porosity,  and  is  greater  the  more  gravel  and  sand  they 
contain.  In  the  following  Table  is  given  the  weight  per 
cubic  foot  of  various  soils  according  to  Schilbler,  and  like- 
wise (in  round  numbers)  the  weight  per  acre  taken  to  the 
depth  of  one  foot  (=43,560  cubic  feet). 

Weight  of  Soils 

per  cubic  foot       per  acre  to  depth 
of  one  foot. 

Dry  silicions  or  calcareous  sand about  110  lbs.  4,792,000 

Half  sand  and  half  clay "  96    "  4,182,000 

Common  arable  land  * "     SO  to    90    "    3,485,000  to  3,920,000 

Heavy  clay "  75    "  3,287,000 

Garden  mold,  rich  in  vegetable  matter. . .     "  70    "  3,049,000 

Peat  soil "     30  to   50    "    1,307,000  to  2,178,000 

From  the  above  figures  we  see  that  sandy  soils,  which 
are  usually  termed  "  light,"  because  they  are  worked  most 
easily  by  the  plow,  are,  in  fact,  the  heaviest  of  aU ;  while 
clayey  land,  which  is  called  "  heavy,"  weighs  less,  bulk 
for  bulk,  than  any  other  soils,  save  those  in  which  vegeta- 
ble matter  predominates.  The  resistance  offered  by  soils 
in  tillage  is  more  the  result  of  adhesiveness  than  of  gravity. 
Sandy  soils,  though  they  contain  in  general  a  less  percent- 
age of  nutritive  matters  than  clays,  may  really  offer  as  good 


*  The  author  is  indebted  to  Prof.  Seely,  of  Middlebury,  Vt.,  for  a  sample  of 
one-fourth  of  a  cubic  foot  of  Wheat  Soil  from  South  Onondaga,  New  York.  The 
cubic  foot  of  this  soil,  Avhen  dry,  weighs  8614  lbs.  The  acre  to  depth  of  one  foot 
weighs  3,768,000  lbs.  This  soil  contains  a  large  proportion  of  slaty  gravel.  A 
rich  garden  soil  of  silicious  sand  that  had  been  heavily  dunged,  time  out  of 
jnind,  Boussingault  found  to  weigh  81  lbs.  av.  per  cubic  foot  (1.3  kilos  per  liter). 
This  would  be  per  acre,  one  foot  deep,  3,528,000  lbs. 


PHYSICAL    CHARACTERS    OF    THE    SOIL.  159 

nourishment  to  crops  as  the  latter,  since  they  present  one- 
half  more  absolute  weight  in  a  given  space. 

Peat  soils  are  light  in  both  senses  in  which  this  word 
is  used  by  agriculturists. 

The  Specific  Gravity  of  Soils  is  the  weight  of  a  given 
bulk  compared  with  the  same  bulk  of  water.  A  cubic 
foot  of  water  weighs  62^  lbs.,  but  comparison  of  this  num- 
ber with  the  numbers  stated  in  the  last  table  expressing 
the  weights  of  a  cubic  foot  of  various  soils  does  not  give 
us  the  true  specific  gravity  of  the  latter,  for  the  reason 
that  these  weights  are  those  of  the  matters  of  the  soil 
contained  in  a  cubic  foot,  but  not  of  a  cubic  foot  of  these 
matters  themselves  exclusive  of  the  air,  occupying  their 
innumerable  interspaces.  When  we  exclude  the  air  and 
take  account  only  of  the  soil,  we  find  that  all  soils,  except 
those  containing  very  much  humus,  have  nearly  the  same 
density.  Schone  has  recently  determined  with  care  the 
specific  gravity  of  14  soils,  and  the  figures  range  from 
2.53  to  2.71.  The  former  density  is  that  of  a  soil  rich  in 
humus,  from  Orenberg,  Russia ;  the  latter  of  a  lime  soil 
from  Jena.  The  density  of  sandy  and  clayey  soils  free  from 
humus  is  2.65  to  2.69.  {Bulletin  de  la  Soc,  Imp.  des 
Naturalistes  de  Moscoii^  1867,  p.  404.)  This  agrees  with 
the  density  of  those  minerals  which  constitute  the  bulk 
of  most  soils,  as  seen  from  the  following  statement  of  their 
specific  gravity,  which  is,  for  quartz,  2.65;  feldspar,  2.62; 
mica,  2.75-3.10  ;  kaolinite,  2.60.  Calcite  has  a  sp.  gr.  of 
2.72 ;  hence  the  greater  density  of  calcareous  soils. 

§2. 

STATE  OF  DIVISION  OF  THE   SOIL  AND  ITS   INFLUENCE  ON 
FERTILITY. 

On  the  surface  of  a  block  of  granite  only  a  few  lichens 
and  mosses  can  exist ;  crush  the  block  to  a  coarse  powder 
and  a  more  abundant  vegetation  can  be  supported  on  it ; 


160  HOW    CKOrS    FEED. 

if  it  is  reduced  to  [i  very  fine  dust  and  duly  vratered,  even 
the  cereal  grains  will  grow  and  perfect  fruit  on  it. 

Magnus  {Jour,  fur  prakt.  Chem.^  L,  70)  caused  barley 
to  germinate  in  pure  feldspar,  which  was  in  one  experi- 
ment coarsely,  in  another  finely,  pulverized.  In  the  coarse 
feldspar  the  plants  greAv  to  a  height  of  15  inches,  formed 
ears,  and  one  of  them  ripened  two  perfectly  formed  seeds. 
In  the  fine  feldspar  the  plants  were  very  decidedly  strong- 
er. One  of  them  attained  a  height  of  20  inches,  and 
j^roduced  four  seeds. 

It  is  true,  as  a  general  rule,  that  all  fertile  soils  contain 
a  large  proportion  of  fine  or  impalpable  matter.  The  soil 
of  the  "  Ree  Ree  Bottom,"  on  the  Scioto  River,  Ohio,  re- 
markable for  its  extraordinary  fertility,  which  has  remamed 
nearly  undiminished  for  60  years,  though  yielding  heavy 
crops  of  wheat  and  maize  without  interruption,  is  char- 
acterized by  the  fineness  of  its  particles.  (D.  A.  Wells, 
jLm,  Jour.  jScL,  XIV,  11.)  In  what  way  the  extreme  di- 
vision of  the  particles  of  the  soil  is  connected  with  its  fer- 
tility is  not  difficult  to  understand.  The  food  of  the  plant 
as  existing  in  the  soil  must  pass  into  solution  either  in  the 
moisture  of  the  soil,  or  in  the  acid  juices  of  the  roots  of 
plants.  In  either  case  the  rapidity  of  its  solution  is  in 
direct  ratio  to  the  extent  of  surface  which  it  exposes. 
The  finer  the  particles,  the  more  abundantly  will  the  plant 
be  supplied  with  its  necessary  nourishment.  In  the  Scioto 
valley  soils,  the  water  which  surrounds  the  roots  of  the 
croj^s  and  the  root-fibrils  themselves  come  in  contact  with 
such  an  extent  of  surface  that  they  are  able  to  dissolve 
the  soil-ingredients  in  as  large  quantity  and  as  rapidly  as 
the  crop  requires.  In  coarse-grained  soils  this  is  not  so 
likely  to  be  the  case.  Soluble  matters  (manures)  must  be 
applied  to  them  by  the  farmer,  or  his  crops  refuse  to  yield 
handsomely. 

It  is  furthermore  obvious,  that,  other  things  being  equal, 
the  finer  the,   articles  of  the  soil  the  more  space  the  grow- 


PHYSICAL    CHAEACTEKS    OF   THE    SOIL.  161 

ing  roots  have  in  which  to  expand  themselves,  and  the 
more  abundantly  are  they  able  to  present  their  absorbent 
surfaces  to  the  supplies  which  the  soil  contains.  The  fine- 
ness of  the  particles  may,  however,  be  excessive.  They 
may  fit  each  other  so  closely  as  to  interfere  with  the 
growth  of  the  roots,  or  at  least  with  the  sprouting  of  the 
seed.     The  soil  may  be  too  compact. 

It  will  presently  appear  that  other  very  important  prop- 
erties of  the  soil  are  more  or  less  related  to  its  state  of 
mechanical  division. 

§    o. 
ABSORPTION  OF  VAPOR  OF  WATER  BY  THE  SOIL. 

The  soil  has  a  power  of  withdrawing  vapor  of  water 
from  the  air  and  condensing  the  same  in  its  pores.  It  is, 
in  other  words,  hygroscopic. 

This  property  of  a  soil  is  of  the  utmost  agricultural  im- 
portance, because,  1st,  it  is  connected  with  the  permanent 
moisture  which  is  necessary  to  vegetable  existence ;  and, 
2d,  since  the  absorption  of  water-vapor  to  some  degree 
determines  the  absorption  of  other  vapors  and  gases. 

In  the  following  table  we  have  the  results  of  a  series 
of  experiments  carried  out  by  Schiibler,  for  the  purpose 
of  determining  the  absorptive  power  of  different  kinds  of 
earths  and  soils  for  vapor  of  water. 

The  column  of  figures  gives  in  thousandths  the  quantity 
of  hygroscopic  moisture  absorbed  in  twenty-four  hours  hj 
the  previously  dried  soil  from  air  confined  over  water, 
and  hence  nearly  saturated  with  vapor. 

Quartz  sand,  coarse 0 

Gyxjsura 1 

Lime  sand „ 3 

Plough  land 23 

Clay  soil,  (60  per  cent  clay) 28 

Slaty  marl 33 

Loam , 35 


162  now    CHOPS    FEED. 

Fine  carbonate  of  lime 35 

Heavy  clay  soil,  (80  per  cent  clay) 41 

Garden  mold,  (7  per  cent  humus) 53 

Pure  clay 49 

Carbonate  of  magnesia  (fine  powder) 83 

Humus 130 

Davy  found  that  one  thousand  parts  of  the  soils  named 

below,  after  having  been  dried  at  212°,  absorbed  during 

one  hour  of  exposure  to  the  air,  quantities  of  moisture  as 

follows : 

Sterile  soil  of  Bagsliot  beath 3 

Coarse  sand 8 

Fine  sand 11 

Soil  from  Mersey,  Essex :_, 18 

Very  fertile  alluvium,  Somersetshire 16 

Extremely  fertile  soil  of  Ormiston,  East  Lothian 18 

An  obvious  practical  result  follows  from  the  facts  ex- 
pressed in  the  above  tables,  viz.:  that  sandy  soils  which 
have  little  attractive  force  for  Avatery  vapor,  and  are  there- 
fore dry  and  arid,  may  be  meliorated  in  this  respect  by 
admixture  with  clay,  or  better  w4th  humus,  as  is  done  by 
dressing  with  vegetable  composts  and  by  green  manuring. 
The  first  table  gives  us  proof  that  gypsum  does  not  exert 
any  beneficial  action  in  consequence  of  directly  attracting 
moisture.  Humus,  or  decaying  vegetable  matter,  it  will 
be  seen,  surpasses  every  other  ingredient  of  the  soil  in 
absorbing  vapor  of  water.  This  is  doubtless  in  some  de- 
gree connected  with  its  extraordinary  porosity  or  amount 
of  surface.  How  the  extent  of  surface  alone  may  act  is 
made  evident  by  comparing  the  absorbent  power  of  car- 
bonate of  lime  in  the  two  states  of  sand  and  of  an  im- 
palpable powder.  The  latter,  it  is  seen,  absorbed  twelve 
times  as  much  vapor  of  water  as  the  former.  Carbonate 
of  magnesia  stands  next  to  humus,  and  it  is  worthy  of 
note  that  it  is  a  very  light  and  fine  powder. 

Finally,  it  is  a  matter  of  observation  that  "  silica  and 
lime  in  the  form  of  coarse  sand  make  the  soil  in  which 
they  predominate  so  dry  and  hot  that  vegetation  perishes 


PHYSICAL    CHARACTERS    OF   THE    SOIL.  163 

from  want  of  moisture;  when,  however,  they  occur  2,'^  fine 
dust^  they  form  too  wet  a  soil,  in  which  plants  suffer  from 
the  opposite  cause." — {HamrrCs  Lctndtoirthschaft.) 

Every  body  has  a  definite  power  of  condensing  moist- 
ure upon  its  surface  or  in  its  pores.  Even  glass,  though 
presenting  to  the  eye  a  perfectly  clean  and  dry  surface,  is 
coated  with  a  film  of  moisture.  If  a  piece  of  glass  be 
weighed  on  a  very  delicate  balance,  and  then  be  wiped 
with  a  clean  cloth,  it  will  be  found  to  weigh  perceptibly 
less  than  before.  Exposed  to  the  air  for  an  hour  or  more, 
it  recovers  the  weight  which  it  had  lost  by  wiping ;  this 
loss  was  water.  (Stas.  Magnus.)  The  surface  of  the 
glass  is  thus  proved  to  exert  towards  vapor  of  water  an 
adhesive  attraction. 

Certain  compounds  familiar  to  the  chemist  attract  water 
with  great  avidity  and  to  a  large  extent.  Oil  of  vitriol, 
phosphoric  acid,  and  chloride  of  calcium,  gain  weight  rap- 
idly when  exposed  to  moist  air,  or  when  placed  contiguous 
to  other  substances  which  are  impregnated  with  moisture. 
For  this  reason  these  compounds  are  employed  for  pur- 
poses of  drying.  Air,  for  example,  is  perfectly  freed  from 
vapor  of  water  by  slowly  traversing  a  tube  containing 
lumps  of  dried  chloride  of  calcium,  or  phosphoric  acid,  or 
by  bubbling  repeatedly  through  oil  of  vitriol  contained 
in  a  suitable  apparatus. 

Solid  substances,  which,  like  chloride  of  calcium,  carbon- 
ate of  potash,  etc.,  gather  water  from  the  air  to  such  an 
extent  as  to  become  liquid,  are  said  to  deliquesce  or  to  be 
deliquescent.  Certain  compounds,  such  as  urea,  the  char- 
acteristic ingredient  of  human  urine,  deliquesce  in  moist 
air  and  dry  away  again  in  a  Avarm  atmosphere. 

Allusion  has  been  made  in  "How  Crops  Grow,"  p.  55, 
to  the  hygroscopic  water  of  vegetation,  which  furnishes 
another  striking  illustration  of  the  condensation  of  water 
in  porous  bodies. 

The  absorption  of  vapor  of  water  by  solid  bodies  is  not 


164  HOW    CHOPS    FEED. 

only  dependent  on  the  nature  of  the  substance  and  its 
amount  of  surface,  but  is  likewise  influenced  by  external 
conditions. 

The  rapidity  of  absorption  depends  upon  the  amount 
of  vapor  present  or  accessible,  and  is  greatest  in  moist 
air. 

The  amount  of  absorption  is  determined  solely  by  tem- 
perature, as  Knop  has  recently  shown,  and  is  unaffected 
by  the  relative  abundance  of  vapor :  i.  e.,  at  a  given  tem- 
perature a  dry  soil  will  absorb  the  same  amount  of  moist- 
ure from  the  air,  no  matter  Avhether  the  latter  be  slightly 
or  heavily  impregnated  with  vapor,  but  will  do  this  the 
more  speedily  the  more  moist  the  surrounding  atmosphere 
happens  to  be. 

In  virtue  of  this  hygroscopic  character,  the  soil  which 
becomes  dry  superficially  during  a  hot  day  gathers  water 
from  the  atmosphere  in  the  cooler  night  time,  even  when 
no  rain  or  dew  is  deposited  upon  it. 

In  illustration  of  the  influence  of  temperature  on  the 
quantity  of  water  absorbed,  as  vapor,  by  the  soil,  we  give 
Knop's  observations  on  a  sandy  soil  from  Moeckern,  Sax- 
ony : 

1,000  parts  of  this  soil  absorbed 

At  55°  F.  13     parts  of  hygroscopic  water. 
"    66°  "  11.9      "     "  "  " 

t(     trtvo    a    1 A  2         "        "  "  " 

«     Qoo    "       c  ^r        "        "  "  " 

Knop  calculates  on  the  basis  of  his  numerous  observa- 
tions that  hair  and  wool,  which  are  more  hygroscopic  than 
most  vegetable  and  mineral  substances,  if  allowed  to  ab- 
sorb what  moisture  they  are  capable  of  taking  up,  contain 
the  following  quantities  of  water,  per  cent^  at  the  temper- 
atures named : 

At  87°  Fah.,    7.7  per  cent. 
"  55°      "      15,5   "       " 
"  32°      "      19.3   "       " 


PHYSICAL    CHARACTEES    OF   THE    SOIL.  165 

Silk  is  sold  in  Europe  by  weight  with  suitable  allowance 
for  hygroscopic  moisture,  its  variable  content  of  which  is 
carefully  determined  by  experiment  in  each  important 
transaction.  It  is  plain  that  the  circumstances  of  sale 
may  affect  the  weight  of  wool  to  10  or  more  per  cent. 


CONDENSATION  OF  GASES  BY  THE  SOIL. 

Adhesion, — In  the  fact  that  soils  and  porous  bodies  gen- 
erally have  a  physical  absorbing  power  for  the  vapor  of 
water,  we  have  an  illustration  of  a  principle  of  very  wide 
application,  viz..  The  surfaces  of  liquid  and  solid  matter 
attract  the  particles  of  other  hinds  of  matter. 

This  force  of  adhesion^  as  it  is  termed,  when  it  acts  up- 
on gaseous  bodies,  overcomes  to  a  greater  or  less  degree 
their  expansive  tendency,  and  coerces  them  into  a  smaller 
space — condenses  them. 

Absorbent  Power  of  Charcoal,  etc. — Charcoal  serves 
to  illustrate  this  fact,  and  some  of  its  most  curious  as  well 
as  useful  properties  depend  upon  this  kind  of  physical 
peculiarity.  Charcoal  is  prepared  from  wood,  itself  ex- 
tremely jDorous,^  by  expelling  the  volatile  constituents, 
whereby  the  porosity  is  increased  to  an  enormous  extent. 

When  charcoal  is  kept  in  a  damp  cellar,  it  condenses  so 
much  vapor  of  water  in  its  pores  that  it  becomes  difficult 
to  set  on  fire.  It  may  even  take  up  one-fourth  its  own 
weight.  When  exposed  to  various  gases  and  volatile 
matters,  it  absorbs  them  in  the  same  manner,  though  to 
very  unequal  extent. 

De  Saussure  was  the  first  to  measure  the  absorbing 
power  of  charcoal  for  gases.  In  his  experunents,  boxwood 
charcoal  was  heated  to  redness  and  plunged  under  mer- 

*  Mitscherlicli  has  calculated  that  the  cells  of  a  cubic  inch  of  boxwood  have 
no  less  than  73  sauare  feet  of  surface. 


166 


HOW    CEOPS    FEED. 


cury  to  cool.  Then  introduced  into  the  various  gases 
named  below,  it  absorbed  as  many  times  its  bulk  of  them, 
as  are  designated  by  the  subjoined  figures: 


Ammonia 90 

Sulphurous  acid 65 

Protoxide  of  nitrogen 40 

Oxj'gen 93^ 

Hydrogen 1% 


Hydrochloric  acid 85 

Hydrosulplmric  acid 55 

Carbonic  acid 35 

Carbonic  oxide 9}{ 

Nitrogen 7^ 


According  to  De  Saussure,  the  absorption  was  comi^lete 
in  24  hours,  except  in  case  of  oxygen,  where  it  continued  for 
a  long  time,  though  with  decreasing  energy.  The  oxygen 
thus  condensed  in  the  charcoal  combined  with  the  carbon 
of  the  latter,  forming  carbonic  acid. 

Stenhouse  more  lately  has  experimented  in  the  same  di- 
rection. From  these  researches  we  learn  that  the  power 
in  question  is  exerted  tov/ards  different  gases  with  very 
unequal  effect,  and  that  different  kinds  of  charcoal  exert 
very  different  condensing  power. 

Stenhouse  found  that  one  gramme  of  dry  charcoal  ab- 
sorbed of  several  gases  the  number  of  cubic  centimeters 
given  below. 


Narne  of  Gas. 


Ammonia 

Hydrochloric  acid 

Hydrosulphuric  acid. 

Sulphurous  acid 

Carbonic  acid 

Oxygen 


Kind  of  Charcoal. 

Wood. 

Peat. 

Animal. 

98.5 

96.0 

43.5 

45.0 

60.0 

30.0 

28.5 

9,0 

32.5 

27.5 

17.5 

14.0 

10.0 

5.0 

0.8 

0.6 

0.5 

The  absorption  or  solution  of  gases  in  water,  alcohol, 
and  other  liquids,  is  analogous  to  this  condensation,  and 
those  gases  which  are  most  condensed  by  charcoal  are  in 
general,  though  not  invariably,  those  which  dissolve  most 
copiously  in  liquids,  (ammonia,  hydrochloric  acid). 

Condensation  ©f  Gases  by  the  Soil. — Reichardt  and 

Blumtritt  have  recently  made  a  minute  study  of  the  kind 
and  amount  of  gases  that  are  condensed  in  the  pores  of 
various  solid  substances,  including  soils  and  some  of  their 


PHYSICAL   CHAEACTEES    OF   THE   SOIL.  167 

ingredients.  {Jour,  far  prcikt,  Chem.,  Bd.  98,  p.  476.) 
Their  results  relate  chiefly  to  these  substances  as  ordinarily- 
occurring  exposed  to  the  atmosphere,  and  therefore  more 
or  less  moist.  The  following  Table  includes  the  more  im- 
portant data  obtamed  by  subjecting  the  substances  to  a 
temperature  of  284°  F.,and  measuring  and  analyzing  the 
gas  thus  expelled, 

100  Gram's  10  Vols.    100  Vols,  of  Gas  contained : 


SuMance : 

ytcn 

in 

vols. 

Nitro- 

Oxy- 

Carbon- 

Car- 

C. C. 

gas. 

gen. 

gen. 

ic  acid. 

bonic 

oxide. 

Charcoal,  air-dry, 

184 

— 

100 

0 

0 

0 

"         moistened  and  dried  i 

again. 

,140 

59 

83 

0 

9 

3 

Peat, 

163 

— 

44 

5 

51 

0 

Garden  soil,  moist, 

14 

20 

04 

3 

24 

9 

"        "     air-dry, 

38 

54 

05 

2 

33 

0 

Hydrated  oxide  of  iron,  air-dry 

375 

309 

23 

4 

70 

0 

Oxide  of  iron,  ignited, 

39 

52 

83 

13 

4 

0 

Hydrated  alumina,  air-dry. 

69 

82 

41 

0 

59 

— 

Alumina,  dried  at  212*^, 

11 

14 

83 

17 

0 

— 

Clay, 

33 

— 

05 

21 

14 

— 

"    long  exposed  to  air, 

23 

39 

70 

5 

25 

— 

"    moistened, 

29 

35 

CO 

6 

34 

— 

River  silt,  air-dry. 

40 

48 

68 

0 

18 

14 

"        "    moistened, 

24 

29 

67 

0 

31 

2 

"        "    again  dried. 

26 

30 

67 

9 

16 

7 

Carbonate  of  lime  (whiting,)  1864, 

43 

52 

100 

0 

0 

— 

"      "              "         1865, 

39 

48 

74 

16 

10 

— 

"           u      u    precipitated, 

,  1864, 

65 

— 

81 

19 

0 

— 

11               i;        i(                    u 

1863, 

51 

52 

77 

15 

8 

— 

Carbonate  of  magnesia, 

729 

125 

64 

7 

29 



Gypsum,  pulverized, 

17 

— 

81 

19 

0 

— 

From  these  figures  we  gather : 

1.  The  gaseous  mixture  which  is  contained  in  the  pores 
of  solid  substances  rarely  has  the  composition  of  the  at- 
mosphere. In  but  two  instances,  viz.,  with  gypsum  and 
precipitated  carbonate  of  lime.,  were  only  oxygen  and  ni- 
trogen absorbed  in  proportions  closely  approaching  those 
of  the  atmosphere. 

2.  Nitrogen  appears  to  be  nearly  always  absorbed  in 
greater  proportion  than  oxygen,  and  is  greatly  condensed 
in  some  cases,  as  by  peat,  hydrated  oxide  of  iron,  and  car- 
bonate of  magnesia. 


168  HOW    CKOPS    FEED. 

3.  Oxygen  is  often  nearly  or  quite  wanting,  as  in  char- 
coal, oxide  of  iron,  alumina,  river  silt,  and  whiting. 

4.  Carbonic  acid,  though  sometimes  wanting  entirely, 
is  usually  abundant  in  the  absorbed  gases. 

5.  In  the  pores  of  charcoal  and  of  soils  containing  de- 
caying organic  matters,  carbonic  acid  is  often  partially  re- 
placed by  carbonic  oxide.  The  experiments,  however,  do 
not  furnish  proof  that  this  substance  is  not  formed  under 
the  influence  of  the  high  temperature  employed  (284°  F.) 
in  expelling  the  gases,  rather  than  by  incomplete  oxidation 
of  organic  matters  at  ordinary  temperatures. 

0.  A  substance,  when  moist,  absorbs  less  gas  than  when 
dry.  In  accordance  with  this  observation,  De  Saussure  no- 
ticed that  dry  charcoal  saturated  with  various  gases  evolv- 
ed a  good  share  of  them  when  moistened  with  water. 
Ground  (and  burnt  ?)  coffee,  as  Babinet  has  lately  stated, 
evolves  so  much  gas  when  drenched  with  water  as  to  burst 
a  bottle  in  which  it  is  confined. 

The  extremely  variable  figures  obtained  by  Blumtritt 
when  operating  with  the  same  substance  (the  figures  given 
in  the  table  are  averages  of  two  or  three  usually  discordant 
results),  result  from  the  general  fact  that  the  proportion 
in  which  a  number  of  gases  are  j^resent  in  a  mixture,  in- 
fluences the  proportion  of  the  individual  gases  absorbed. 
Thus  while  charcoal  or  soil  will  absorb  a  large  amount  of 
ammonia  from  the  pure  gas,  it  will  take  up  but  traces  of 
this  substance  from  the  atmosphere  of  which  ammonia  is 
but  an  infinitesimal  ingredient. 

So,  too,  charcoal  or  soil  saturated  with  ammonia  by  ex- 
posure to  the  unmixed  gas,  loses  nearly  all  of  it  by  stand- 
ing in  the  air  for  some  time.  This  is  due  to  the  fact  that 
gases  attract  each  other ^  and  the  composition  of  the  gas 
condensed  in  a  porous  body  varies  perpetually  with  the 
variations  of  composition  in  the  surrounding  atmosphere. 

It  is  especially  the  water-gas  (vapor  of  water)  which  is 
a  fluctuating  ingredient  of  the  atmosphere,  and  one  which 


PHYSICAL    CHAEACTERS    OF   THE    SOIL.  169 

is  absorbed  by  porous  bodies  in  the  largest  quantity. 
This  not  only  displaces  other  gases  from  their  adhesion  to 
solid  surfaces,  but  by  its  own  attractions  modifies  these 
adhesions. 

Reichardt  and  Blumtritt  take  no  account  of  water-gas, 
except  in  the  few  experiments  where  the  substances  wei  e 
purposely  moistened.  In  all  their  trials,  however,  moist- 
ure was  present,  and  had  its  quantity  been  estimated, 
doubtless  its  influence  on  the  extent  and  kind  of  absorp- 
tion would  have  been  strikingly  evident  throughout. 

Ammonia  and  carbonate  of  ammonia  in  the  gaseous 
form  are  absorbed  from  the  air  by  the  dry  soil,  to  a  less 
degree  than  by  a  soil  that  is  moist,  as  will  be  noticed  fully 
hereafter. 

Chemical  Aciloa  mdticed  hj  Adiiesiois.— This  physical 
property  often  leads  to  remarkable  chemical  effects ;  in 
other  words,  adhesion  exalts  or  brings  into  play  the  force 
of  affinity.  When  charcoal  absorbs  those  emanations 
from  putrefying  animal  matters  which  we  scarcely  know, 
save  by  their  intolerable  odor  and  poisonous  influence,  it 
causes  at  the  same  time  their  rapid  and  complete  oxida- 
tion ;  and  hence  a  piece  of  tainted  meat  is  sweetened  by 
covering  it  with  a  thin  layer  of  powdered  charcoal.  As 
Stenhouse  has  shown,  the  carcass  of  a  small  animal  may 
be  kept  in  a  living-room  during  the  hottest  weather  with- 
out giving  off  any  putrid  odor,  provided  it  be  surrounded 
on  all  sides  by  a  layer  of  powdered  charcoal  an  inch  or 
more  thick.  Thus  circumstanced,  it  simply  smells  of  am- 
77ionia^  and  its  destructible  parts  are  resolved  directly  in- 
to water,  carbonic  acid,  free  nitrogen,  and  ammonia,  pre- 
cisely as  if  they  were  burned  in  a  furnace,  and  without 
the  appearance  of  any  of  the  effluvium  that  ordinarily 
arises  from  decaying  flesh. 

The  metal  platinum  exhibits  a  remarkable  condensing 
power,  which  is  manifest  even  with  the  polished  surface  of 
foil  or  wire ;    but   is  most   striking  when  the  metal   is 
8 


170  HOW    CEOPS    FEED. 

brought  to  the  condition  of  sponge,  a  form  it  assumes 
when  certain  of  its  compounds  (e.  g.  ammonia-chloride  of 
platinum)  are  decomposed  by  heat,  or  to  the  more  finely 
divided  state  of  platinum  black.  The  latter  is  capable  of 
condensing  from  100  to  250  times  its  volume  of  oxygen, 
according  to  its  mode  of  preparation  (its  porosity  ?) ;  and 
for  this  reason  it  possesses  intense  oxidizing  power,  so  that, 
for  example,  when  it  is  brought  into  a  mixture  of  oxygen 
and  hydrogen,  it  causes  them  to  unite  explosively.  A  jet 
of  hydrogen  gas,  allowed  to  play  on  platinum  sponge,  is 
almost  instantly  ignited — a  fact  taken  advantage  of  in 
Dobereiner's  hydrogen  lamp. 

The  oxidizing  powers  of  platinum  are  much  more  vig- 
orous than  those  of  charcoal.  Stenhouse  has  proposed 
the  use  of  platinized  charcoal  (charcoal  ignited  after  moist- 
ening with  solution  of  chloride  of  platinum)  as  an  escha- 
rotic  and  disinfectant  for  foul  ulcers,  and  has  shown  that 
the  foul  air  of  sewers  and  vaults  is  rendered  innocuous 
when  filtered  or  breathed  through  a  layer  of  this  material.* 

Chemical  Action  a  Result  of  tlie  Porosity  of  tlie  Soil. 
— From  these  significant  facts  it  has  been  inferred  that  the 
soil  by  virtue  of  the  extreme  porosity  of  some  of  its  ingre- 
dients is  the  theater  of  chemical  changes  of  the  utmost 
importance,  which  could  not  transpire  to  any  sensible  ex- 
tent but  for  this  high  division  of  its  particles  and  the  vast 
surface  they  present. 

The  soil  absorbs  putrid  and  other  disagreeable  effluvia, 
and  undoubtedly  oxidizes  them  like  charcoal,  though,  per- 
haps, with  less  energy  than  the  last  named  substance,  as 
would  be  anticipated  from  its  inferior  porosity.  Garments 
which  have  been  rendered  disgusting  by  the  fetid  secre- 
tions of  the  skunk,  may  be  "  sweetened,"  i.  e.  deprived  of 

*  Platinum  does  not  condense  hydrogen  gas  ;  but  the  metal  Palladium,  which 
occurs  associated  with  platinum,  has  a  most  astonishing  absorptive  power  for 
hydrogen,  being  able  to  take  up  or  "  occlude"  900  times  its  volume  of  the  gas, 
(Graham,  Proceedings  Roy,  JSoc,  1868^  p.  422.] 


■    ABSORBENT   POWEE    OF    SOILS.  171 

odor,  by  burying  tliem  for  n,  few  days  in  the  earth.  The 
Indians  of  this  country  are  said  to  sweeten  the  carcass  of 
the  skunk  by  the  same  process,  when  needful,  to  fit  it  for 
their  food.  Dogs  and  foxes  bury  bones  and  meat  in  the 
ground,  and  afterward  exhume  them  in  a  state  of  com- 
parative freedom  from  offensive  odor. 

When  human  excrements  are  covered  with  fine  dry 
earth,  as  in  the  "  Earth  Closet "  system,  all  odor  is  at  once 
suppressed  and  never  reappears.  At  the  most,  besides  an 
"  earthy "  smell,  an  odor  of  ammonia  appears,  resulting 
from  decomposition,  which  appears  to  proceed  at  once  to 
its  ultimate  results  without  admitting  of  the  formation  of 
any  intermediate  offensive  compounds. 

Dr.  Angus  Smith,  having  frequently  observed  the  pres- 
ence of  nitrates  in  the  water  of  shallow  town  wells,  sus- 
pected that  the  nitric  acid  was  derived  from  animal  mat- 
ters, and  to  test  this  view,  made  experiments  on  the  action 
of  filters  of  sand,  and  other  porous  bodies,  upon  solutions 
of  different  animal  and  vegetable  matters.  He  found 
that  in  such  circumstances  oxidation  took  place  most  rap- 
idly— the  nitrogen  of  organic  matters  being  converted  in- 
to nitric  acid,  the  carbon  and  hydrogen  combining  with 
oxygen  at  the  same  time.  Thus  a  solution  of  yeast,  which 
contained  no  nitric  acid,  after  being  passed  through  a 
filter  of  sand,  gave  abundant  evidence  of  salts  of  this  acid. 
Colored  solutions  were  in  this  way  more  or  less  decolor- 
ized. Water,  rendered  brown  by  peaty  matter,  was  found 
to  be  purified  by  filtration  through  sand.'^ 

§   5. 

POWEK  OF  SOILS  TO  EEMOVE  DISSOLVED  SOLIDS  FROM 
THEIR  SOLUTIONS. 

Action  of  Sand  upon  Saline  Solutions. — It  has  long 
been  known  that  simple  sand  is  capable  of  partially  re- 

*  This  account  of  Dr.  Smith's  experiments  is  quoted  from  Prof.  Way's  paper 
"On  the  Power  of  Soils  to  Absorb  Manure."  {Jour,  Boy.  Ag.  Sac.  of  England^ 
XI,  p.  317.) 


172  HOW    CROPS    FEED. 

moving  saline  matters  from  their  solutions  in  water.  Lord 
Bacon,  in  his  "  Sylva  Sylvarum,"  speaks  of  a  method  of 
obtaining  fresh  water,  which  was  practised  on  the  coast 
of  Barbary.  "  Digge  a  hole  on  the  sea-shore  somewhat 
above  high-water  mark  and  as  deep  as  low-water  mark, 
which,  when  the  tide  cometh,  will  be  filled  with  water 
fresh  and  potable."  He  also  remarks  "  to  have  read  that 
trial  hath  been  made  of  salt-water  passed  through  earth 
through  ten  vessels,  one  within  another,  and  yet  it  hath 
not  lost  its  saltness  as  to  become  potable ; "  but  when 
"  drayiied  through  twenty  vessels,  hath  become  fresh." 

Dr.  Stephen  Hales,  in  a  paper  read  before  the  Royal 
Society  in  1739,  on  "  Some  attempts  to  make  sea-water 
wholesome,"  mentions  on  the  authority  of  Mr.  Boyle  God- 
frey that  "sea-water,  being  filtered  through  stone  cisterns, 
the  first  pint  that  runs  through  will  be  pure  water  having 
no  taste  of  the  salt,  but  the  next  pint  will  be  salt  as  usual." 

Berzelius  found  upon  filtering  solutions  of  common  salt 
through  sand,  that  the  portions  Vv^hich  first  passed  were 
quite  free  from  saline  impregnation.  Matteucci  extended 
this  observation  to  other  salts,  and  found  that  the  solu- 
tions Avhen  filtered  through  sand  were  diminished  in  den- 
sity, showing  a  detention  by  the  sand  of  certain  quantities 
of  the  salt  operated  upon.* 

Action  of  lIiiMiis  OM  Saline  Solutions. — Heiden  {Hoff- 
mam-Cs  Jakreshericht^  1866,  p.  29)  found  that  peat  and 
various  preparations  of  th.e  humic  acids,  when  brought  in- 
to solutions  of  chloride  of  potassium  and  chloride  of  am- 
monium, remove  a  portion  of  these  salts  from  the  liquid, 
leaving  the  solutions  perceptibly  weaker.  The  removed 
salts  v/ere  for  the  most  part  readily  dissolved  by  a  small 
quantity  of  water.  W.  Schumacher  {Soff.  Jahres.^  1867, 
p.  18)  observed  that  humus,  artificially  prepared  by  the 

*  These  statements  of  Bacon,  Hales,  Berzelius,  and  Matteucci,  are  derived 
from  Prof.  Way's  paper  "  On  the  Power  of  Soils,  etc."  {Jour.  Roy.  Ag.  Soc.  of 
Eng.,  XI,  31G.) 


ABSORBENT  PO^VER    OF    SOILS.  173 

action  of  oil  of  vitriol  on  sugar,  when  placed  in  ten  times 
its  quantity  of  solutions  of  various  salts  (containing  about 
-V  per  cent  of  solid  matter)  absorbed  of  sulphates  of  soda 
and  ammonia,  and  chlorides  of  calcium  and  ammonium, 
about  2  per  cent ;  of  sulphate  of  potash  4  per  cent ;  and  of 
phosphate  of  soda  10  per  cent.  Schumacher  also  noticed 
that  sulj^hate  of  potash  is  able  to  expel  sulphate  of  ammo- 
nia from  humic  acid  which  has  been  saturated  with  the 
latter  salt,  but  that  the  latter  cannot  displace  the  former. 
Ill  Schumacher's  experiments,  pure  water  freely  dissolved 
the  salts  absorbed  by  the  humic  acid. 

Explanation. — Let  us  consider  what  occurs  in  the  act 
of  solution  and  in  this  separation  of  soluble  matters  from 
a  liquid.  The  difference  between  the  solid  and  the  liquid 
state,  so  far  as  we  can  define  it,  lies  in  the  unequal  cohe- 
sion of  the  particles.  Cohesion  prevails  in  solids,  and  op- 
poses freedom  of  motion  among  the  particles.  In  liquids, 
cohesion  is  not  altogether  overcome  but  is  greatly  weak- 
ened, and  the  particles  move  easily  upon  each  other. 
When  a  lump  of  salt  is  put  into  water,  the  cohesion  that 
otherwise  maintains  its  particles  in  the  solid  state  is  over- 
come by  the  attraction  of  adhesion,  which  is  mutually  ex- 
erted between  them  and  the  particles  of  water,  and  the 
salt  dissolves.  If  now  into  the  solution  of  salt  any  in- 
soluble solid  be  placed  v/hich  the  liquid  can  wet  (adhere 
to)  its  particles  will  exert  adhesive  attraction  for  the  par- 
ticles of  salt,  and  the  tendency  of  the  latter  will  be  to 
concentrate  somewhat  upon  the  surface  of  the  solid. 

If  the  solid,  thus  introduced  into  a  solution,  be  exceed- 
ingly porous,  or  otherwise  present  a  great  amount  of  sur- 
face, as  in  case  of  sand  or  humus,  this  tendency  is  propor- 
tionately heightened,  and  a  separation  of  the  dissolved 
substance  may  become  plainly  evident  on  proper  examina- 
tion. When,  on  the  other  hand,  the  solid  surface  is  rela- 
tively small,  no  weakening  of  the  solution  may  be  percep- 
tible by  ordinary  means.     Doubtless  the  glass  of  a  bottle 


174  HOW    CEOPS    FEED. 

containing  brine  concentrates  the  latter  where  the  two 
are  in  contact,  though  the  effect  may  be  difficult  to  dem- 
onstrate. 

Defecating  Acllon  ©f  Charcoal  ©a  Solsitions. — Char- 
coal manifests  a  strong  surface  attraction  for  various 
solid  substances,  and  exhibits  this  power  by  overcoming 
the  adhesion  they  have  to  the  particles  of  water  when  dis- 
solved in  that  fluid.  If  ink,  solution  of  indigo,  red  wine, 
or  bitter  ale,  be  agitated  some  time  with  charcoal,  the 
color,  and  in  the  case  of  ale,  the  bitter  principle,  will  be 
taken  up  by  the  charcoal,  leaving  the  liquid  colorless  and 
comparatively  tasteless.  Water,  which  is  impure  from 
putrefying  organic  matters,  is  sweetened,  and  brown  sugars 
are  whitened  by  the  use  of  charcoal  or  bone-black.  In 
case  of  bone-black,  the  finely  divided  bone-earth  (phos- 
phate of  lime)  assists  the  action  of  the  charcoal. 

Flsing  of  Bye-Stuffs. — The  familiar  process  of  dyeing 
depends  upon  the  adhesion  of  coloruig  matters  to  the  fiber 
of  textile  fabrics.  Wool  steeped  in  solution  of  indigo  at- 
taches the  pigment  permanently  to  its  fibers.  Silk  in  the 
same  way  fastens  the  particles  of  rosaniliae,  which  consti- 
tutes the  magenta  dye.  Many  colors,  e.  g.  madder  and 
logwood,  which  will  not  adhere  themselves  directly  to 
cloth,  are  made  to  dye  by  the  use  of  mordants — substances 
like  alumina,  oxide  of  tin,  etc. — which  have  adhesion  both 
to  the  fabric  and  the  pigment. 

Absorptive  Fower  of  Clay. — These  effects  of  charcoal 
and  of  the  fibers  of  cotton,  etc.,  are  in  great  part  identical 
with  those  previously  noticed  in  case  of  sand  and  humus. 
Their  action  is,  however,  more  intense,  and  the  effects 
are  more  decided.  Charcoal,  for  example,  that  has  ab- 
sorbed a  pigment  or  a  bitter  principle  from  a  liquid,  will 
usually  yield  it  up  again  to  tbe  same  or  a  stronger  solvent. 
In  some  instances,  how-ever,  as  in  dyeing  with  simple  col- 
ors, matters  are  fixed  in  a  state  of  great  permanence  by 


ABSORBENT   POWER    OF    SOILS.  175 

the  absorbent ;  and  in  otliers,  as  wbere  mordants  are  used, 
chemical  combinations  supervene,  which  possess  extraordi- 
nary stability. 

Many  facts  are  known  which  show  that  soils,  or  certain 
of  their  ingredients,  have  a  fixing  power  like  that  of  char- 
coal and  textile  fibers.  It  is  a  matter  of  common  expe- 
rience that  a  few  feet  or  yards  of  soil  intervening  between 
a  cess-pool  or  dung-pit,  and  a  well,  preserves  the  latter 
against  contamination  for  a  longer  or  shorter  period. 

J.  P.  Bronner,  of  Baden,  in  a  treatise  on  "  Grape  Cul- 
ture in  South  Germany,"  published  in  1836,  fii'st  mentions 
that  dung  liquor  is  deodorized,  decolorized,  and  rendered 
nearly  tasteless  by  filtration  through  garden  earth.  Mr. 
Huxtable,  of  England,  made  the  same  observation  in  1848, 
and  Prof.  Way  and  others  have  published  extended  in- 
vestigations on  this  extremely  important  subject. 

Prof.  Way  informs  us  that  he  filled  a  long  tube  to  the 
depth  of  18  inches  with  Mr.  Huxtable's  light  soil,  mixed 
with  its  own  bulk  of  white  sand.  "  Upon  this  filter-bed 
a  quantity  of  highly  offensive  stinking  tank  water  was 
poured.  The  liquid  did  not  pass  for  several  hours,  but 
ultimately  more  than  1  ounce  of  it  passed  quite  clear^  free 
from  smell  or  taste,  except  a  peculiar  earthy  smell  and 
taste  derived  from  the  soil."  Similar  results  were  obtain- 
ed by  acting  upon  putrid  human  urine,  upon  the  stinking 
water  in  which  flax  had  been  steeped,  and  upon  the  water 
of  a  London  sewer. 

Prof  Way  found  that  these  effects  were  not  strikingly 
manifested  by  pure  sand,  but  appeared  when  clay  was 
used.  He  found  that  solutions  of  coloring  matters,  such 
as  logwood,  sandal- wood,  cochineal,  litmus,  etc.,. when  fil- 
tered through  or  shaken  up  with  a  portion  of  clay,  are 
entirely  deprived  of  color.  {Jour.  Roy.  Ag.  Soc.  of 
Mig.,Xl,  p.  364.) 

These  effects  of  clay  or  clayey  matters,  like  the  fixing 
power  of  cotton  and  woolen  stuffs  upon  pigments,  must 


176  HOW    CROPS    FEED. 

be  regarded  for  the  most  part  as  j^nrely  physical.  There 
are  other  results  of  the  action  of  the  soil  on  saline  solu- 
tions, which,  though  perhaps  influenced  by  simple  physical 
action,  are  prepoiideratingly  chemical  in  their  aspect. 
These  eflects,  which  manifest  themselves  by  chemical  de- 
compositions and  substitutions,  will  be  fully  discussed  in 
a  subsequent  chapter,  p.  333. 

g  6. 

PEEMEABILITT  OF   SOILS   TO   LIQUID  WATER.    IMBIBITION. 
CAPILLARY  POWER. 

The  fertility  of  the  soil  is  greatly  influenced  by  its  de- 
portment toward  water  in  the  liquid  state. 

A  soil  is  permeahle  to  water  when  it  allows  that  liquid 
to  soak  into  or  run  through  it.  To  be  permeable  is  of 
course  to  be  porous.  On  the  size  of  the  pores  depends  its 
degree  of  permeability.  Coarse  sands,  and  soils  which 
have  few  but  fer^e  pores  or  interspaces,  allow  water  to 
run  through  them  readily — water  percolates  them.  "When, 
instead  of  running  through,  the  water  is  largely  absorbed 
and  held  by  the  soil,  the  latter  is  said  to  possess  great 
capillary  power  y  such  a  soil  has  many  and  minute  pores. 
The  cause  of  capillarity  is  the  same  surface  attraction 
which  has  been  already  under  notice. 

When  a  narrow  vial  is  partly  filled  with  water,  it  will 
be  seen  that  the  liquid  adheres  to  its  sides,  and  if  it  be  not 
more  than  one-half  inch  in  diameter,  the  surface  of  the 
liquid  will  be  curved  or  concave.  In  a  very  narrow  tube 
the  liquid  will  rise  to  a  considerable  height.  In  these 
cases  the  surface  attraction  of  the  glass  for  the  water  neu- 
tralizes or  overcomes  the  weight  of  (earth's  attraction  for) 
the  latter. 

The  pores  of  a  sponge  raise  and  hold  water  in  them,  in 
the  same  way  that  these  narrow  (capillary*)  tubes  sup- 

*  From  capiUus,  the  Latin  word  for  hair,  because  as  fine  as  hair ;  (but  a  hair  is 
no  tube,  as  is  often  supposed.) 


PERMEABILITY    OF    SOILS    XO    LIQUID    WATEPw  177 

port  it.  When  a  body  has  pores  so  fine  (surfaces  so  near 
each  other)  that  their  surface  attraction  is  greater  than 
the  gravitating  tendency  of  water,  then  the  body  will  im- 
bibe and  hold  water — will  exhibit  capillarity ;  a  lump  of 
salt  or  sugar,  a  lamp-wick,  are  familiar  examples.  When 
the  pores  of  a  body  are  so  large  (the  surfaces  so  distant) 
that  they  cannot  fill  themselves  or  keep  themselves  full, 
the  body  allows  the  water  to  run  through  or  to  percolate. 

Sand  is  most  easily  permeable  to  water,  and  to  a  higher 
degree  the  coarser  its  particles.  Clay,  on  the  other  hand, 
is  the  least  penetrable,  and  the  less  so  the  purer  and  more 
plastic  it  is. 

When  a  soil  is  too  coarsely  porous,  it  is  said  to  be  leachy 
or  hungry.  The  rains  that  fall  upon  it  quickly  soak 
through,  and  it  shortly  becomes  dry.  On  such  a  soil,  the 
manures  that  may  be  applied  in  the  s^^ring  are  to  some  de- 
gree washed  down  below  the  reach  of  vegetation,  and  in 
the  droughts  of  summer,  plants  suffer  or  perish  from  want 
of  moisture. 

When  the  texture  of  a  soil  is  too  fine, — its  pores  too 
small, — as  happens  in  a  heavy  clay,  the  rains  penetrate  it 
too  slowly ;  they  flow  off  the  surface,  if  the  latter  be  in- 
clined, or  remain  as  pools  for  days  and  even  weeks  in  the 
hollows. 

In  a  soil  of  proper  texture  the  rains  neither  soak  off  into 
the  under-earth  nor  stagnate  on  the  surface,  but  the  soil 
always  (except  in  excessive  wet  or  drought)  maintains 
the  moistness  which  is  salutary  to  most  of  our  cultivated 
plants. 

Movements  of  Water  in  the  Soil.— If  a  wick  be  put 
into  a  lamp  containing  oil,  the  oil,  by  capillary  action, 
gradually  permeates  its  whole  length,  that  which  is  above 
as  well  as  that  below  the  surface  of  the  liquid.  When  the 
lamp  is  set  burning,  the  oil  at  the  flame  is  consumed,  and 
as  each  particle  disappears  its  place  is  supplied  by  a  new 
one,  until  the  lamp  is  empty  or  the  flame  extinguished. 
8* 


178  HOW    CKOPS    FEED. 

Something  quite  analogous  occurs  in  the  soil,  by  which 
the  plant  (corresponding  to  the  flame  in  our  illustration)  is 
fed.  The  soil  is  at  once  lamp  and  wick,  and  the  water  of 
the  soil  represents  the  oil.  Let  evaporation  of  water  from 
the  surface  of  the  soil  or  of  the  plant  take  the  place  of 
the  combustion  of  oil  from  a  wick,  and  the  matter  stands 
thus :  Let  us  suppose  dew  or  rain  to  have  saturated  the 
ground  with  moisture  for  some  depth.  On  recurrence  of 
a  dry  atmosphere  with  sunshine  and  wind,  the  surface  of 
the  soil  rapidly  dries ;  but  as  each  particle  of  water  es- 
capes (by  evaporation)  into  the  atmosphere,  its  place  is 
supplied  (by  capillarity)  from  the  stores  below.  The  as- 
cending water  brings  along  with  it  the  soluble  matters  of 
the  soil,  and  thus  the  roots  of  plants  are  situated  in  a 
stream  of  their  appropriate  food.  The  movement  proceeds 
in  this  way  so  long  as  the  surface  is  drier  than  the  deeper 
soil.  When,  by  rain  or  otherwise,  the  surface  is  saturated, 
it  is  like  letting  a  thin  stream  of  oil  run  upon  the  apex  of 
the  lamp-wick — no  more  evaporation  into  the  air  can  oc- 
cur, and  consequently  there  is  no  longer  any  ascent  of 
water;  on  the  contrary,  the  water,  by  its  own  weight, 
penetrates  the  soil,  and  if  the  underlying  ground  be  not 
saturated  with  moisture,  as  can  happen  where  the  subter- 
ranean fountains  yield  a  meagre  supply,  then  capillarity 
will  aid  gravity  in  its  downward  distribution. 

It  is  certain  that  a  portion  of  the  mineral  matters,  and, 
perhaps,  also  some  organic  bodies  which  feed  the  plant, 
are  more  or  less  freely  dissolved  in  the  water  of  the  soil. 
So  long  as  evaporation  goes  on  from  the  surface,  so  long 
there  is  a  constant  upward  flow  of  these  matters.  Those 
portions  which  do  not  enter  vegetation  accumulate  on  or 
near  the  surface  of  the  ground ;  when  a  rain  falls,  they  are 
washed  down  again  to  a  certain  depth,  and  thus  are  kept 
constantly  changing  their  place  with  the  water,  which  is 
the  vehicle  of  their  distribution.  In  regions  where  rain 
falls  periodically  or  not  at  all,  this  upAvard  flow  of  the  soil- 


PERMEABILITY    OF    SOILS    TO    LIQUID    WATEK.  179 

water  often  causes  an  accumulation  of  salts  on  the  surface 
of  the  ground.  Thus  in  Bengal  many  soils  which  in  the 
wet  season  produce  the  most  luxuriant  crops,  during  the 
rainless  portion  of  the  year  become  covered  with  white 
crusts  of  saltpeter.  The  beds  of  nitrate  of  soda  that  are 
found  in  Peru,  and  the  carbonate  of  soda  and  other  salts 
which  incrust  the  deserts  of  Utah,  and  often  fill  the  air 
with  alkaline  dust,  have  accumulated  in  the  same  manner. 
So  in  our  western  caves  the  earth  sheltered  from  rains  is 
saturated  with  salts — epsom-salts,  Glauber's-salts,  and  salt- 
peter, or  mixtures  of  these.  Often  the  rich  soil  of  gardens 
is  slightly  incrusted  in  this  manner  in  our  summer  weather ; 
but  the  saline  matters  are  carried  into  the  soil  with  the 
next  rain. 

It  is  easy  to  see  how,  in  a  good  soil,  capillarity  thus 
acts  in  keeping  the  roots  of  plants  constantly  immersed  in 
a  stream  of  water  or  moisture  that  is  now  ascending,  now 
descending,  but  never  at  rest,  and  how  the  food  of  the 
plant  is  thus  made  to  circulate  around  the  organs  fitted 
for  absorbing  it. 

The  same  causes  that  maintain  this  perpetual  supply  of 
water  and  food  to  the  plant  are  also  efficacious  in  con- 
stantly preparing  new  supplies  of  food.  As  before  ex- 
plained, the  materials  of  the  soil  are  always  undergoing 
decomposition,  whereby  the  silica,  lime,  phosphoric  acid, 
potash,  etc.,  of  the  insoluble  fragments  of  rock,  become 
soluble  in  water  and  accessible  to  the  plant.  Water 
charged  with  carbonic  acid  and  oxygen  is  the  chief  agent 
in  these  chemical  changes.  The  more  extensive  and  rapid 
the  circulation  of  water  in  the  soil,  the  more  matters  will 
be  rendered  soluble  in  a  given  time,  and,  other  things  be- 
ing equal,  the  less  will  the  soil  be  dependent  on  manures 
to  keep  up  its  fertility. 

Capacity  of  ImMMtion.  Capillary  Power. — No  mat- 
ter how  favorable  the  structure  of  the  soil  may  be  to  the 


180  HOW    CROPS    FEED. 

circulation  of  water  in  it,  no  continuous  upward  movement 
can  take  j^lace  without  evaporation.  The  ease  and  rapid- 
ity of  evaporation,  while  mainl}^  depending  on  the  condi- 
tion of  the  atmosphere  and  on  the  sun's  heat,  are  to  a  cer- 
tain degree  influenced  by  the  soil  itself.  We  have  already 
seen  that  the  soil  possesses  a  power  of  absorbing  watery 
vapor  from  the  atmosphere,  a  power  which  is  related  both 
to  the  kind  of  material  that  forms  the  soil  and  to  its  state 
of  division.  This  absorptive  power  oj^poses  evaporation. 
Again,  different  soils  manifest  widely  different  capacities 
for  imbibing  liquid  water — capacities  mainly  connected 
with  their  porosity.  Obviously,  too,  the  quantity  of  liquid 
in  a  given  volume  of  soil  affects  not  only  the  rapidity, 
but  also  the  duration  of  evaporation. 

The  following  tables  by  Schtibler  illustrate  the  peculi- 
arities of  different  soils  in  these  respects.  The  first  col- 
umn gives  the  percentages  of  liquid  loater  absorbed  by 
the  completely  dry  soil.  In  these  experiments  the  soils 
were  thoroughly  wet  with  water,  the  excess  allowed  to 
drip  off,  and  the  increase  of  weight  determined.  In  the 
second  column  are  given  the  percentages  of  water  that 
evaporated  dm-ing  the  space  of  four  hours  from  the  satu- 
rated soil  spread  over  a  given  surface : 

Quartz  sand 25  88.4 

Gypsum 27  71.7 

Lime  sand 29  75.9 

Slaty  marl 34  68.0 

Clay  soil,  (sixty  per  cent  clay,) 40  52.0 

Loam 51  45. 7 

Plough  land 52  82.0 

Heavy  clay,  (eighty  per  cent  clay,) 61  34.9 

Pure  gray  clay 70  31.9 

Fine  carbonate  of  lime 85  28.0 

Garden  mould 89  24.3 

Humus 181  25.5 

Fine  carbonate  of  magnesia 256  10.8 . 

It  is  obvious  that  these  two  columns  express  nearly  the 
same  thing  in  different  ways.     The  amount  of  water  re- 


PEKME ABILITY    OF    SOILS    TO    LIQUID    WATEE.  181 

tained  increases  from  quartz  sand  to  magnesia.  The  rap- 
idity of  drying  in  the  air  diminishes  in  the  same  direction. 
Some  observations  of  Zenger  ( Wilda^s  Centrcdblatt, 
1858,  1,  430)  indicate  the  influence  of  the  state  of  division 
of  a  soil  on  its  power  of  imbibing  water.  In  the  subjoin- 
ed table  are  given  in  tlie  first  column  the  per  cent  of  wa- 
ter imbibed  by  various  soils  which  had  been  brought  to 
nearly  the  same  degree  of  moderate  fineness  by  sifting  off" 
both  the  coarse  and  the  fine  matter ;  and  the  second  col- 
umn gives  the  amounts  imbibed  by  the  same  soils,  reduced 
to  a  high  state  of  division  by  pulverization. 


Coai'se. 

Fine. 

Quartz  sand, 

26.0 

535 

Mali  (used  as  fertilizer,) 

30.3 

54.5 

Marl,  uuderlying  peat, 

39.0 

48.5 

Brick  clay, 

66.3 

57.5 

Moor  soil, 

104.5 

101.0 

Aim  (lime-sinter,) 

108.3 

70.4 

Aim  soil. 

178.3 

103.5 

Peat  dust. 

377.0 

368.5 

The  effects  of  pulverization  on  soils  whose  particles  are 
compact  is  to  increase  the  surface,  and  increase  to  a  cor- 
responding degree  the  imbibing  power.  On  soils  consist- 
ing of  porous  particles,  like  lime-sinter  and  peat,  pulver- 
ization destroys  the  porosity  to  some  extent  and  diminishes 
the  amount  of  absorption.  The  first  class  of  soils  are 
probably  increased  in  bulk,  the  latter  reduced,  by  grinding. 

Wilhelm,  {Wilda's  Centralblatt,  1866,  1,  118),  in  a 
series  of  experiments  on  various  soils,  confirms  the  above 
results  of  Zenger.  He  found,  e.  g.,  that  a  garden  mould 
imbibed  114  per  cent,  but  when  pulverized  absorbed  but 
62  per  cent. 

To  illustrate  the  difi*erent  properties  of  various  soils  for 
which  the  farmer  has  but  one  name,  the  fact  may  be  ad- 
duced that  while  Schiibler,  Zenger,  and  Wilhelm  found 
the  imbibing  power  of  "  clay  "  to  range  between  40  and 
70  per  cent,  Stoeckhardt  examined  a  "  clay  "  from  Saxony 


182  now  CROPS  feed 

tliat  held  150  -per  cent  of  water.  So  the  humus  of  Schiib- 
ler  imbibed  181  per  cent ;  the  peat  of  Zenger,  377  per  cent ; 
while  Wilhelm  examined  a  very  porous  peat  that  took  up 
519  per  cent.  These  differences  are  dependent  mainly  on 
the  mechanical  texture  or  porosity  of  the  material. 

The  want  of  capillary  retentive  power  for  water  in  the 
case  of  coarse  sand  is  undeniably  one  of  the  chief  reasons 
of  its  unfruitfulness.  The  best  soils  possess  a  medium  re- 
tentive power.  In  them,  therefore,  are  best  united  the 
conditions  for  the  regular  distribution  of  the  soil-water 
under  all  circumstances.  In  them  this  process  is  not  hin- 
dered too  much  either  by  wet  or  dry  weather.  The  re- 
taining power  of  humus  is  seen  to  be  more  than  double 
that  of  clay.  This  result  might  appear  at  first  sight  to 
be  in  contradiction  to  ordinary  observations,  for  we  are 
accustomed  to  see  water  standing  on  the  surface  of  clay 
but  not  on  humus.  It  must  be  borne  in  mind  that  clay, 
from  its  imperviousness,  holds  water  like  a  vessel,  the  wa- 
ter remaining  apparent ;  but  humus  retains  it  invisibly, 
its  action  being  nearly  like  that  of  a  sponge. 

One  chief  cause  of  the  value  of  a  layer  of  humus  on 
the  surface  of  the  soil  doubtless  consists  in  this  great  re- 
taining power  for  water,  and  the  success  that  has  attended 
the  practice  of  green  manuring,  as  a  means  of  renovating 
almost  worthless  shifting  sands,  is  in  a  great  degree  to  be 
attributed  to  this  cause.  The  advantages  of  mulching  are 
explained  in  the  same  way. 

Soils  which  are  over-rich  in  humus,  especially  those  of 
reclaimed  peat-bogs,  have  some  detrimental  peculiarities 
deserving  notice.  Stoeckhardt  ( Wtlda'^s  CentralblaU, 
1858,  2,  22)  examined  the  soil  of  a  cultivated  moor  in 
Saxony,  which,  when  moist,  had  an  imbibing  power  of 
60-69°  I j^.  After  being  thoroughly  dried,  however,  it  lost 
its  adhesiveness,  and  the  imbibing  power  fell  to  26-30°  |o. 

It  is  observed  in  accordance  with  these  data  that  such 
soils  retain  water  late  in  spring ;    and  when  they  become 


CHANGES    OF   THE   BULK    OP   THE    SOIL.  183 

very  dry  in  summer  tliey  are  slow  to  take  up  water  again, 
so  that  rain-water  stands  on  the  surface  for  a  considerable 
time  without  penetrating,  and  when,  after  some  days,  it 
is  soaked  up,  it  remains  injuriously  fong.  Light  rains 
after  drought  do  little  immediate  good  to  such  soils, 
while  heavy  rains  always  render  them  too  wet  and  cold, 
unless  they  are  suitably  ameliorated.  The  same  is  trae  to 
a  less  degree  of  heavy,  compact  clays. 

§  'T. 

CHANGES  OF  THE  BULK  OF  THE  SOIL  BY  DRYING  AND 
FROST. 

TIjc  Sliriakiag  of  Soils  on  Drying  is  a  matter  of  no 
little  practical  importance.  This  shrinking  is  of  course 
offset  by  an  increase  of  bulk  when  the  soil  becomes  wet. 
In  variable  weather  we  have  therefore  constant  changes 
of  volume  occurring. 

Soils  rich  in  humus  experience  these  changes  to  the 
greatest  degree.  The  surfaces  of  moors  often  rise  and 
fall  with  the  wet  or  dry  season,  through  a  space  of  sev- 
eral inches.  In  ordinary  light  soils,  containing  but  little 
humus,  no  change  of  bulk  is  evident.  Otherwise,  it  is  in 
clay  soils  that  shrinking  is  most  perceptible ;  smce  these 
soils  only  dry  superficially,  they  do  not  apj^ear  to  settle 
much,  but  become  full  of  cracks  and  rifts.  Heavy  clays 
may  lose  one-tenth  or  more  of  their  volume  on  drying, 
and  since  at  the  same  time  they  harden  about  the  rootlets 
which  are  imbedded  in  them,  it  is  plain  that  these  indis- 
pensable organs  of  the  plant  must  thereby  be  ruptured 
during  the  protracted  dry  weather.  Sand,  on  the  other 
hand,  does  not  change  its  bulk  by  wetting  or  drying,  and 
when  present  to  a  considerable  extent  in  the  soil,  its  par- 
ticles, being  interposed  between  those  of  the  clay,  prevent 
the  adhesion  of  the  latter,  so  that,  although  a  sandy  loam 
shrinks  not  inconsiderably  on  drying,  yet  the  lines  of  sepa- 


184  now  CKOPS  feed. 

ration  arc  vastly  more  numerous  and  less  wide  than  in 
purer  clays.  Such  a  soil  does  not  "  cake,"  but  remains 
friable  and  powdery. 

Marly  soils  (containing  carbonate  of  lime)  are  especially 
prone  to  fall  to  a  fine  powder  during  drying,  since  the 
carbonate  of  lime,  which,  irKe  sand,  shrinks  very  little,  is 
itself  in  a  state  of  extreme  division,  and  therefore  more 
effectually  separates  the  clayey  23articles.  The  unequal 
shrinking  of  these  two  intimately  mixed  ingredients  ac- 
complishes a  perfect  pulverization  of  such  soils.  On  the 
cold,  heavy  soils  of  Upper  Lusatia,  in  Germany,  the  appli- 
cation of  lime  has  been  attended  with  excellent  results, 
and  the  larger  share  of  the  benefit  is  to  be  accounted  for 
by  the  improvement  in  the  texture  of  those  soils  which 
follows  liming.  The  carbonate  of  lime  is  considerably 
soluble  in  water  charged  with  carbonic  acid,  as  is  the  wa- 
ter of  a  soil  containing  vegetable  matter,  and  this  agency 
of  distribution,  in  connection  with  the  mechanical  opera- 
tions of  tillage,  must  in  a  short  time  effect  an  intimate 
mixture  of  the  lime  with  the  whole  soil.  A  tenacious  clay 
is  thus  by  a  heavy  liming  made  to  approach  the  condition 
of  a  friable  marl. 

lleavmg  by  Frost, — Soils  which  imbibe  much  water, 
especially  clay  and  peat  soils,  have  likewise  the  disagree- 
able property  of  being  heaved  by  frost.  The  expansion, 
by  freezing,  of  the  liquid  water  they  contain,  separates  the 
particles  of  soil  from  each  other,  raises,  in  fact,  the  surface 
for  a  considerable  height,  and  thus  ruptures  the  roots  of 
grass  and  especially  of  fall-sowed  grain.  The  lifting  of 
fence  posts  is  due  to  the  same  cause. 

§8. 

ADHESIVENESS  OF  THE  SOIL. 

In  the  language  of  the  farm  a  soil  is  said  to  be  heavy 
or  light,  not  as  it  weighs  more  or  less,  but  as  it  is  easy  or 


ADHESIYEXESS    O?    THE    SOIL.  185 

difficult  to  work.  The  state  of  dryness  has  great  influence 
on  this  quality.  Sand,  lime,  and  humus  have  very  little 
adhesion  when  dry,  but  considerable  when  wet.  Soils  in 
which  they  predominate  are  usually  easy  to  work.  But 
clay  or  impalpable  matter  has  entirely  different  characters, 
upon  which  the  tenacity  of  a  soil  almost  exclusively  de- 
pends. Dry  "clay,"  Vv^hen  powdered,  has  hardly  more 
consistence  than  sand,  but  v/hen  thoroughly  moistened  its 
particles  adhere  together  to  a  soft  and  plastic,  but  tena- 
cious mass ;  and  in  drymg  away,  at  a  certain  point  it  be- 
comes very  hard,  and  requires  a  good  deal  of  force  to 
penetrate  it.  In  this  condition  it  offers  great  resistance  to 
the  instruments  used  in  tillage,  and  when  thrown  up  by 
the  plow  it  forms  lumps  which  require  repeated  harrow- 
ings  to  break  them  down.  Since  the  adhesiveness  of  the 
soil  depends  so  greatly  upon  the  quantity  of  water  con- 
tained in  it,  it  follows  that  thorough  draining,  combined 
with  deep  tillage,  whereby  sooner  or  later  the  stiffest  clays 
become  readily  permeable  to  water,  must  have  the  best 
effects  in  making  such  soils  easy  to  work. 

The  English  practice  of  burning  clays  speedily  accom- 
plishes the  same  purpose.  When  clay  is  burned  and  then 
crushed,  the  particles  no  longer  adhere  tenaciously  to- 
gether on  moistening,  and  the  mass  does  not  acquire  again 
the  unctuous  plasticity  peculiar  to  unburned  clay. 

Mixing  sand  with  clay,  or  incorporating  vegetable  mat- 
ter w^ith  it,  or  liming,  serves  to  separate  the  particles 
from  each  other,  and  thus  remedies  too  great  adhesiveness. 

The  considerable  expansion  of  water  in  the  act  of  solid- 
ifying (one-fifteenth  of  its  volume)  has  already  been  no- 
ticed as  an  agency  in  reducing  rocks  to  powder.  In  the 
same  way  the  alternate  freezing  and  thawing  of  the  water 
which  impregnates  the  soil  during  the  colder  part  of  the 
year  plays  an  important  part  in  overcoming  its  adhesion. 
The  effect  is  apparent  in  the  spring,  immediately  after 
"  the  frost  leaves  the  ground,"  and  is  very  considerable, 


188  HOW    CROPS    FEED. 

fully  one-third  of  the  resistance  of  a  clay  or  loam  to  the 
plow  thus  disappearing,  according  to  Schiibler's  experi- 
ments. 

Tillage,  when  carried  on  with  the  soil  in  a  wet  condi- 
tion, to  some  extent  neutralizes  the  effects  of  frost,  espe- 
cially in  tenacious  soils. 

Fall-plowing  of  stiff  soils  has  been  recommended,  in 
order  to  expose  them  to  the  disintegrating  effects  of  frost. 

§  9- 
RELATIONS  OF  THE  SOIL  TO  HEAT. 

The  relations  of  the  soil  to  heat  are  of  the  utmost  im- 
portance in  affecting  its  fertility.  The  distribution  of 
plants  is,  in  general,  determined  by  differences  of  mean 
temperature.  In  the  same  climate  and  locality,  however, 
we  find  the  farmer  distinguishing  between  cold  and  warm 
soils. 

The  Temperature  of  tlie  Soil  varies  to  a  certain  depth 
with  that  of  the  air ;  yet  its  changes  occur  more  slowly, 
are  confined  to  a  considerably  narrower  range,  and  dimin- 
ish downward  in  rapidity  and  amount,  until  at  a  certain 
depth  a  point  is  reached  where  the  temperature  is  invari- 
able. 

In  summer  the  temperature  of  the  soil  is  higher  in  day- 
time than  that  of  the  air ;  at  night  the  temperature  of  the 
surface  rapidly  falls,  especially  when  the  sky  is  clear. 

In  temperate  climates,  at  a  depth  of  three  feet,  the  tem- 
perature remains  unchanged  from  day  to  night ;  at  a  depth 
of  20  feet  the  annual  temperature  varies  but  a  degree  or 
two ;  at  75  feet  below  the  surface,  the  thermojneter  re- 
mains perfectly  stationary.  In  the  vaults  of  the  Paris 
Observatory,  80  feet  deep,  the  temperature  is  50°  Fahren- 
heit. In  tropical  regions  the  point  of  nearly  unvarying 
temperature  is  reached  at  a  depth  of  one  foot. 


KELATIOXS    OF    THE    SOIL    TO    HEAT.  187 

The  mean  annual  temperature  of  the  soil  is  the  same  as, 
or  in  higher  latitudes  a  degree  above,  that  of  the  air.  The 
nature  and  position  of  the  soil  must  considerably  influence 
its  temperature 

Sources  of  tiie  Heat  of  tlie  Soil, — The  sources  of  that 
heat  which  is  found  in  the  soil  are  tliree,  viz. :  First,  the 
original  heat  of  the  earth ;  second,  the  chemical  process 
of  oxidation  or  decay  going  on  within  it ;  and  third,  an 
external  one,  the  rays  of  the  sun 

The  earth  has  within  itself  a  source  of  heat,  which 
maintains  its  interior  at  a  high  temperature;  but  which 
escapes  so  rapidly  from  the  surface  that  the  soil  would  be 
constantly  frozen  but  for  the  external  supply  of  heat  from 
the  sun. 

The  heat  evolved  by  the  decay  of  organic  matters  is 
not  inconsiderable  in  porous  soils  containing  much  vegeta- 
ble remains ;  but  decay  cannot  jDroceed  rapidly  until  the 
external  temperature  has  reached  a  point  favorable  to 
vegetation,  and  therefore  this  source  of  heat  probably  has 
no  appreciable  effect,  one  way  or  the  other,  on  the  welfare 
of  the  plant.  The  warmth  of  the  soil,  so  far  as  it  favors 
vegetable  growth,  appears  then  to  depend  exclusively  on 
the  heat  of  the  sun. 

The  direct  rays  of  the  sun  are  the  immediate  cause  of 
the  warmth  of  the  earth's  surface.  The  temperature  of 
the  soil  near  the  surface  changes  progressively  with  the 
seasons ;  but  at  a  certain  depth  the  loss  from  the  interior 
and  the  gain  from  the  sun  compensate  each  other,  and,  as 
has  been  previously  mentioned,  the  temperature  remains 
unchanged  throughout  the  year. 

Daily  Changes  ©f  Temperature, — ^During  the  day  the 
sun's  heat  reaches  the  earth  directly,  and  is  absorbed  by 
the  soil  and  the  solid  objects  on  its  surface,  and  also  by 
the  air  and  water.  But  these  different  bodies,  and  also 
the  different  kinds  of  soil,  have  very  different  ability  to 
absorb  or  become  warmed  by  the  sun's  heat.     Air  and 


183  IIOYr    CROPS    FEED. 

Avater  are  almost  incapable  of  being  warmed  by  heat  ap- 
plied above  tbem.  Through  the  air,  heat  radiates  without 
being  absorbed.  Solid  bodies  which  have  dull  and  porous 
surfaces  absorb  heat  most  rapidly  and  abundantly.  The 
soil  and  solid  bodies  become  warmed  according  to  their 
individual  capacity,  and  from  them,  the  air  receives  the 
heat  which  warms  it.  From  the  moist  surface  of  the  soil 
goes  on  a  rapid  evaporation  of  water,  which  consumes  *  a 
large  amount  of  heat,  so  that  the  temperature  of  the  soil 
is  not  rapidly  but  gradually  elevated.  The  ascent  of  wa- 
ter from  the  subsoil  to  supply  the  place  of  that  evaporat- 
ed, goes  on  as  before  described.  When  the  sun  declines, 
the  process  diminishes  in  intensity,  and  when  it  sets,  the 
reverse  takes  place.     The  heat  that  had  accumulated  on 


*  WTien  a  piece  of  ice  is  placed  in  a  vessel  whose  temperature  is  increasing, 
by  means  of  a  lamp,  at  the  rate  of  one  degree  of  the  thermometer  every  minute, 
it  will  be  found  that  the  temperature  of  the  ice  rises  until  it  attains  32°.  When 
this  point  is  reached,  it  begins  to  melt,  but  doos  not  suddenly  become  fluid :  the 
melting  goes  on  very  gradually.  A  thermometer  placed  in  the  water  remains 
constantly  at  32°  so  long  as  a  fragment  of  ice  is  present.  The  moment  the  ice 
disappears,  the  temperature  begins  to  rise  again,  at  the  rate  of  one  degree  per 
minute.  The  time  during  which  the  temperature  of  the  ice  and  water  remains 
at  32°  is  140  minutes.  During  each  of  these  minutes  one  degree  of  heat  enters 
the  mixture,  but  is  not  indicated  by  the  thermometer— the  mercury  remains  sta- 
tionary ;  140°  of  heat  have  thus  passed  into  the  ice  and  become  hidden,  latent  ; 
at  the  same  time  the  solid  ice  has  become  liquid  water.  The  difference,  then, 
between  ice  and  water  consists  in  the  heat  that  is  latent  in  the  latter.  If  we  now 
proceed  with  the  above  experiment,  allowing  the  heat  to  increase  with  the  same 
rapidity,  we  find  that  the  temperature  of  the  water  rises  constantly  for  180  min- 
utes. The  thermometer  then  indicates  a  temperature  of  212°,  (32+180,)  and  the 
water  boils.  Proceeding  with  the  experiment,  the  water  evaporates  away,  but 
the  thermometer  continues  stationary  so  long  as  any  liquid  remains.  After  the 
lapse  of  972  minutes,  it  is  completely  evaporated.  Water  in  becoming  steam 
rerjders,  therefore,  still  another  portion,  9T2°,  of  heat  latent.  The  heat  latent  in 
steam  is  indispensable  to  the  existence  of  the  latter.  If  this  heat  be  removed 
by  bringing  the  steam  into  a  cold  space,  water  is  reproduced.  If,  by  means  of 
pressure  or  cold,  steam  be  condensed,  the  heat  originally  latent  in  it  becomes 
sensible, /ree,  and  capable  of  atfectiug  the  thermometer.  If,  also,  water  be  con- 
verted into  ice,  as  much  heat  is  evolved  and  made  sensible  as  was  absorbed  and 
made  latent.  It  is  seen  thus  that  the  processes  of  liquefaction  and  vaporization 
are  cooling  processes  ;  for  the  heat  rendered  latent  by  them  must  be  derived  from 
surrounding  objects,  and  thus  these  become  cooled.  On  the  contrary,  solidifica- 
tion, freezing,  and  vapor-condensation,  are  ivarmmg  processes,  since  in  them 
large  quantities  of  heat  ce"ise  to  be  latent  and  are  made  sensible,  thus  warming 
surrounding  bodies. 


RELATIONS    OF    THE    SOIL   TO    HEAT.  189 

the  surface  of  the  earth  radiates  into  the  cooler  atmos- 
phere and  planetary  space ;  the  temperature  of  the  surface 
rapidly  diminishes,  and  the  air  itself  becomes  cooler  by 
convection. "^  As  the  cooling  goes  on,  the  vapor  suspend- 
ed in  the  atmosphere  begins  to  condense  upon  cool  objects, 
while  its  latent  heat  becoming  free  hinders  the  too  sudden 
reduction  of  temperature.  The  condensed  water  collects 
in  drops — it  is  dew ;  or  in  the  colder  seasons  it  crystallizes 
as  hoar-frost. 

The  deposition  of  liquid  water  takes  place  not  on  the 
surface  of  the  soil  merely,  but  within  it,  and  to  that  depth 
in  which  the  temperature  falls  during  the  night,  viz.,  12 
to  18  inches.  (Krutzsch  observed  the  temperature  of  a 
garden  soil  at  the  depth  of  one  foot,  to  rise  3°  F.  on  a 
May  day,  from  9  A.  M.  to  7  P.  M.) 

Since  the  air  contained  in  the  interstices  of  the  soil  is  at 
a  little  depth  saturated  with  aqueous  vapor,  it  results  that 
the  slightest  reduction  of  temperature  must  at  once  occa- 
sion a  deposition  of  water,  so  that  the  soil  is  thus  supplied 
with  moisture  independently  of  its  hygroscopic  power. 

Conditions  that  Affect  the  Temperature  of  the  Soil.— 
The  special  nature  of  the  soil  is  closely  connected  with 
the  maintenance  of  a  uniform  temperature,  with  the  pre- 
vention of  too  great  heat  by  day  and  cold  by  night,  and 
with  the  watering  of  vegetation  by  means  of  dew.  It  is, 
however,  in  many  cases  only  for  a  little  space  after  seed- 
time that  the  soil  is  greatly  concerned  in  these  processes. 
So  soon  as  it  becomes  covered  wdth  vegetation,  the  char- 


*  Thougli  liquids  and  gases  are  almost  perfect  non-conductors  of  lieat,  yet  it  can 
diffuse  through  them  rapidly,  if  advantage  be  taken  of  the  fact  that  by  heating  they 
expand  and  therefore  become  specifically  lighter.  If  heat  be  applied  to  the  upper 
surface  of  liquids  or  gases,  they  remain  for  a  long  time  nearly  unaffected ;  if 
it  be  applied  beneath  them,  the  lower  layers  of  particles  become  heated  and  rise, 
their  place  is  supplied  by  others,  and  so  currents  upward  and  downward  are 
established,  whereby  the  heat  is  rapidly  and  uniformly  distributed.  This  process 
of  convection  can  rarely  have  any  influence  in  the  soil.  What  we  have  stated 
concerning  it  shows,  however,  in  what  way  the  atmosphere  may  constantly  act 
in  removing  heat  from  the  surface  of  the  soil. 


190  HOYf    CEOPS    FEED. 

acter  of  the  latter  determines  to  a  certain  degree  the  na- 
ture of  the  atmospheric  changes.  In  case  of  many  crojDS, 
the  soil  is  but  partially  covered,  and  its  peculiarities  are 
then  of  direct  influence  on  its  temperature. 

Relatioii  ©f  Temperature  to  Color  and  Texture.— It 
is  usually  stated  that  black  or  dark-colored  soils  are  sooner 
warmed  by  the  sun's  rays  than  those  of  lighter  color,  and 
remain  constantly  of  a  higher  temperature  so  long  as  the 
sun  acts  on  them.  An  elevation  of  several  degrees  in  the 
temperature  of  a  light-colored  soil  may  be  caused  by 
strewing  its  surface  w^ith  peat,  charcoal  powder,  or  vege- 
table mould.  To  this  influence  may  be  partly  ascribed 
the  following  facts.  Lampadius  was  able  to  ripen  melons, 
even  in  the  coolest  summers,  in  Freiberg,  Saxony,  by 
strewing  a  coating  of  coal  dust  an  inch  deep  over  the  sur- 
face of  the  soil.  In  Belgium  and  on  the  Rhine,  it  is  found 
that  the  grape  matures  best,  when  the  soil  is  covered  with 
fragments  of  black  clay  slate. 

According  to  Creuze-Latouche,  the  vineyards  along  the 
river  Loire  grow  either  upon  a  light-colored  calcareous 
soil,  or  upon  a  dark  red  earth.  These  two  kinds  of  soil 
often  alternate  with  each  other  within  a  little  distance, 
and  the  character  of  the  wine  produced  on  them  is  remark- 
ably connected  with  the  color  of  the  earth.  On  the  light- 
colored  soils  only  a  weak,  white  wine  can  be  raised  to  ad- 
vantage, while  on  contiguous  dark  soils  a  strong  claret  of 
fine  quality  is  made.  (Gasparin,  Cours  cV  Agriculture,  1, 
103.) 

Girardin  found  in  a  series  of  experiments  on  the  cultiva- 
tion of  potatoes,  that  the  time  of  their  ripening  varied 
eight  to  fourteen  days,  according  to  the  color  of  the  soil. 
He  found  on  August  25th,  in  a  very  dark  humus  soil, 
twenty-six  varieties  ripe;  in  sandy  soil,  twenty;  in  clay, 
nineteen;  and  in  white  lime  soil,  only  sixteen.  It  is  not 
difficult,  however,  to  indicate  other  causes  that  will  ac- 
count in  part  for  the  results  of  Girardin. 


EELATIOI^S    OF    THE    SOIL   TO    HEAT.  191 

Schtibler  made  observations  on  the  temperatures  at- 
tained by  various  dry  soils  exposed  to  the  sun's  rays, 
according  as  their  surfaces  were  blackened  by  a  thin 
sprinkling  of  lamp-black  or  whitened  by  magnesia.  His 
results  are  given  in  columns  1  and  2  of  the  following  table 
{vide  p.  196,)  from  which  it  is  seen  that  the  dark  surface 
was  warmed  13°  to  14°  more  than  the  white.  We  like- 
wise notice  that  the  character  of  the  very  surface  deter- 
mines the  degree  of  warmth,  for,  under  a  sprinkling  of 
lamp-black  or  magnesia,  all  the  soils  experimented  with 
became  as  good  as  identical  in  their  absorbing  power  for 
the  sun's  heat. 

The  observations  of  Malaguti  and  Durocher  prove  that 
the  peculiar  temperature  of  the  soil  is  not  always  so 
closely  related  to  color  as  to  other  qualities.  They  studied 
the  thermometric  characters  of  the  following  soils,  viz. : 
Garden  earth  of  dark  gray  color, — a  mixture  of  sand  and 
gravel  with  about  five  per  cent  of  humus ;  a  grayish- 
white  quartz  sand ;  a  grayish-brown  granite  sand ;  a  fine 
light-gray  clay  (pipe  clay) ;  a  yellow  sandy  clay ;  and, 
finally,  four  lime  soils  of  different  physical  qualities. 

It  was  found  that  when  the  exposure  was  alike,  the 
dark-gray  granite  sand  became  the  warmest,  and  next  to 
this  the  grayish-white  quartz  sand.  The  latter,  notwith- 
standing its  lighter  color,  often  acquired  a  higher  temper- 
ature at  a  depth  of  four  inches  than  the  former,  a  fact  to 
be  ascribed  to  its  better  conducting  power.  The  hlack 
soils  never  became  so  warm  as  the  two  just  mentioned. 
After  the  black  soils,  the  others  came  in  the  following  or- 
der :  garden  soil ;  yellow  sandy  clay ;  pipe  clay ;  lime 
soils  having  crystalline  grains ;  and,  lastly,  a  pulverulent 
chalk  soil. 

To  show  what  different  degrees  of  warmth  soils  may 
acquire,  under  the  same  circumstances,  the  following  max- 
imum temperatures  may  be  adduced :  At  noon  of  a  July 
day,  when  the  temperature  of  the  air  was  90°,  a  therm om- 


192  HOW    CHOPS    FEED. 

eter  j)laced  at  a  dej)tli  of  a  little  more  than  one  inch,  gave 
these  results : 

In  quartz  snnd 126° 

In  cryslalline  lime  soil .115° 

In  garden  soil 114° 

In  yellow  sandy  clay 100° 

In  pipe  clay ., 94° 

In  chalk  soil 87* 

Here  we  observe  a  difference  of  nearly  40°  in  the  noon- 
day temperature  of  the  coarse  quartz  and  the  chalk  soil. 
Malaguti  and  Durocher  found  that  the  temperature  of  the 
garden  soil,  just  below  the  surface,  was,  on  the  average 
of  day  and  night  together,  6°  Fahrenheit  higher  than  that 
of  the  air,  but  that  this  higher  temperature  diminished  at 
a  greater  depth.  A  thermometer  buried  four  inches  indi- 
cated a  mean  temperature  only  3°  above  that  of  the  at- 
mosphere. 

The  experimenters  do  not  mention  the  influence  of  wa- 
ter in  aifecting  these  results  ;  they  do  not  state  the  degree 
of  dryness  of  these  soils.  It  Avill  be  seen,  however,  that 
the  warmest  soils  are  those  that  retain  least  water,  and 
doubtless  something  of  the  slowness  with  which  the  fine 
soils  increase  in  warmth  is  connected  with  the  fact  that 
they  retain  much  w^ater,  which,  in  evaporating,  appropri- 
ates and  renders  latent  a  large  quantity  of  heat. 

The  chalk  soil  is  seen  to  be  the  coolest  of  all,  its  tem- 
perature in  these  observations  being  three  degrees  lower 
than  that  of  the  atmosphere  at  noonday.  In  hot  climates 
this  coolness  is  sometimes  of  great  advantage,  as  appears 
to  happen  in  Spain,  near  Cadiz,  where  the  Sherry  vine- 
yards flourish.  "  The  Don  said  the  Sherry  wine  district 
was  very  small,  not  more  than  twelve  miles  square.  The 
Sherry  grape  grew  only  on  certain  low,  chalky  hills,  where 
the  earth  being  light-colored,  is  not  so  much  burnt;  did 
not  chap  and  split  so  much  by  the  sun  as  darker  and 
heavier  soils  do.  A  mile  beyond  these  hills  the  grape  de- 
teriorates."~(Dickens'  Household  WorcU  Nov.  13, 1858.) 


RELATIONS    OF    THE    SOIL   TO    HEAT.  193 

In  Explanation  of  these  observations  we  must  recall  to 
mind  the  fact  that  all  bodies  are  capable  of  absorbing  and 
radiating  as  well  as  reflecting  heat.  These  properties,  al- 
though never  dissociated  from  color,  are  not  necessarily 
dependent  upon  it.  They  chiefly  depend  upon  the  char- 
acter of  the  surface  of  bodies.  Smooth,  polished  surfaces 
absorb  and  radiate  heat  least  readily ;  they  reflect  it  most 
perfectly.  Kadiation  and  absorption  are  opposed  to  each 
other,  and  the  power  of  any  body  to  radiate,  is  precisely 
equal  to  its  faculty  of  absorbing  heat. 

It  must  be  understood,  however,  that  bodies  may  differ 
in  their  power  of  absorbing  or  radiating  heat  of  different 
degrees  of  intensity.  Lamp-black  absorbs  and  radiates 
heat  of  all  intensities  in  the  same  degree.  White-lead 
absorbs  heat  of  low  intensity  (such  as  radiates  from  a  ves- 
sel filled  with  boiling  water)  as  fully  as  lamp-black,  but 
of  the  intense  heat  of  a  lamp  it  absorbs  only  about  one- 
half  as  much.  Snow  seems  to  resemble  white-lead  in  this 
respect.  If  a  black  cloth  or  black  paper  be  spread  on  the 
surface  of  snow,  upon  which  the  sun  is  shining,  it  will 
melt  much  faster  under  the  cloth  than  elsewhere,  and  this, 
too,  if  the  cloth  be  not  in  contact  with,  but  suspended 
above,  the  snow.  In  our  latitude  every  one  has  had  op- 
portunity to  observe  that  snow  thaws  most  rapidly  when 
covered  by  or  lying  on  black  earth.  The  people  of  Cham- 
ouni,  in  the  Swiss  Alps,  strew  the  surface  of  their  fields 
with  black-slate  powder  to  hasten  the  melting  of  the  snow. 
The  reason  is  that  snow  absorbs  heat  of  low  intensity 
with  greatest  facility.  The  heat  of  the  sun  is  converted 
from  a  high  to  a  low  intensity  by  being  absorbed  and  then 
radiated  by  the  black  material.  But  it  is  not  color  that 
determines  this  difference  of  absorptive  power,  for  indigo 
and  Prussian  blue,  though  of  nearly  the  same  color,  have 
very  different  absorptive  powers.  So  far,  however,  as  our 
observations  extend,  it  appears  that,  usually,  dark-colored 
soils  absorb  heat  most  rapidly,  and  that  the  sun's  rays 
9 


194  now  CHOPS  peed. 

have  least  effect  on  liglit-colored  soils.      (See  the  table  on 
p.  196.) 
Tlie  Rapidity  of  Ciiange  of  Temperature  independently 

of  color  or  moisture  has  been  determined  on  a  number  of 
soils  by  Schilbler.  A  given  volume  of  dry  soil  was  heat- 
ed to  145°,  a  thermometer  was  placed  in  it,  and  the  time 
was  observed  which  it  required  to  cool  down  to  70°,  the 
temperature  of  the  atmosphere  being  61°.  The  subjoined 
table  gives  his  results.  In  one  column  are  stated  the 
times  of  cooling^  in  another  the  relative  power  of  retaining 
heat  or  capacity  for  heat,  that  of  lime  sand  being  assumed 
as  100. 


Lime  sand 3  hours 

Quartz  sand 3  " 

Potter's  clay 2  " 

Gypsum 2  " 

ciay  loam 2  " 

Clay  plow  land 2  " 

Heavy  clay 2  " 

Pure  gray  clay 2  " 

Garden  earth 2  " 

rine  carb.  lime 2  " 

Humus 1  " 

Mag-nesia 1  " 


oOmin... 

...100 

27  " 

....95.6 

41  ".... 

....76.9 

34  ".... 

....73.8 

30  ".... 

71.8 

07   " 

70.1 

24  '\... 

....68.4 

19  ".... 

....66.7 

16  ".... 

....64.8 

10  ".... 

....61.3 

43  ".... 

....49.0 

20  ".... 

....38.0 

It  is  seen  that  the  sandy  soils  cool  most  slowly,  then 
follow  clays  and  heavy  soils,  and  lastly  comes  humus. 

The  order  of  cooling  above  given  is  in  all  respects 
identical  with  that  of  warming,  provided  the  circumstances 
are  alike.  In  other  words  these  soils,  containing  no  moist- 
ure, or  but  little,  and  exposed  to  heat  of  low  intensity, 
would  be  raised  through  a  given  range  of  temperature  in 
the  same  relative  times  that  they  fall  through  a  given 
number  of  degrees. 

It  is  to  be  particularly  noticed  that  dark  humus  and  white 
magnesia  are  very  closely  alike  in  their  rate  of  cooling, 
and  cool  rapidly ;  while  white  lime  sand  stands  at  the  op- 
posite extreme,  requiring  twice  as  long  to  cool  to  the  samo 
extent.     These  facts  strikingly  illustrate  the  great  differv 


KELATIO]S"S    OF    THE    SOIL    TO    HEAT.  195 

ence  between  the  absorption  of  radiant  beat  of  low  inten- 
sity or  its  communication  by  conduction  on  one  band,  and 
that  of  high  intensity  like  the  beat  of  the  sun  on  tbe  other. 

Metentloa  ©f  Heati— Otber  circumstances  being  equal, 
tbe  power  of  retaining  beat  (slowness  of  cooling)  is  the 
greater,  tbe  greater  tbe  weigbt  of  a  given  bulk  of  soil, 
i,  e.,  tbe  larger  and  denser  its  particles. 

A  soil  covered  witb  gravel  cools  much  more  slowly 
tban  a  sandy  surface,  and  tbe  heat  wbicb  it  collects  during  a 
sunny  day  it  carries  farther  into  tbe  nigbt ;  bence  gravelly 
soils  are  adapted  for  sucb  crops  as  are  liable  to  fail  of  rip- 
ening in  cool  situations,  especially  grapes,  as  bas  been 
abundantly  observed  in  practice. 

Color  is  without  influence  on  tbe  loss  of  beat  from  tbe 
soil  by  radiation,  because  tbe  beat  is  of  low  intensity. 
Tbe  porosity  or  roughness  of  tbe  surface  (extent  of  sur- 
face) determines  cooling  from  this  cause.  Dew,  wbicb  is 
deposited  as  the  result  of  cooling  by  radiation  of  beat  into 
tbe  sky,  forms  abundantly  on  grass  and  growing  vege- 
tation, and  on  vegetable  mould,  but  is  more  rarely  met  witb 
on  coarse  sand  or  gravel. 

Influence  of  Moisture  ©n  the  Temperature  of  the  Soil. 
— ^All  soils,  when  thoroughly  wet,  seem  to  be  nearly  alike 
in  their  power  of  absorbing  and  retaining  warmth.  This 
is  due  to  tbe  fact  that  the  capacity  of  water  for  Jieat  is 
much  greater  than  that  of  the  soil.  We  have  seen  that 
lime  sand  and  quartz  sand  are  the  slowest  of  all  the  in- 
gredients of  soils  to  suffer  changes  of  temperature  when 
exposed  to  a  given  source  of  beat.     (See  table,  p.  194.) 

N"ow,  water  is  nine  times  slower  than  quartz  in  being 
affected  by  changes  of  temperature,  and  as  the  entire  sur- 
face of  the  wet  soil  is  water,  which  is,  besides,  a  nearly 
l^erfect  non-conductor  of  beat,  we  can  understand  that  ex- 
ternal warmth  must  affect  it  slowly. 

Again,  the  immense  consumption  of  heat  in  the  forma- 
tion of  vapor  (see  note,  p.  188)  must  prevent  tbe  wet  soil 


196 


HOW    CKOPS    FEED. 


from  ever  acquiring  the  temperature  it  shortly  attains 
when  dry. 

From  this  cause  the  difference  in  temperature  between 
dry  and  wet  soil  may  often  amount  to  from  10°  to  18°. 

On  this  point,  again,  Schubler  furnishes  us  with  the  re- 
sults of  his  experiments.  Columns  4  and  5  in  the  table 
below  give  the  temperatures  which  the  thermometer  at- 
tained when  its  bulb  was  immersed  in  various  soils,  both 
wet  and  dry,  each  having  its  natural  color.  (Columns  1 
and  2  are  referred  to  on  p.  191.) 


Magnesia,  pure  white 108 

Fine  carbonate  of  lime,  white 109 

Gypsum,  bright  white-gray 110, 

Plow  land,  gray 107. 

Sandy  clay,  yellowish 108 , 

Quartz  sand,  bright  yellowish-gray 109. 

Loam,  yellowish 107. 

Lime  sand,  whitish-gray 109. 

Heavy  clay  soil,  yellowish-gray 107. 

Pure  clay,  bluish-gray 106 . 

Garden  mould,  blackish-gray !108. 

Slaty  marl,  brownish-red !108. 

Humus,  brownish-black !108. 


12  3         4  5  6 

Surface.  Surface. 


Whit-  Black-  Differ 


ened.    ened. 


121.3= 
122.9° 
124.3° 
122.0° 
121.6° 
123.6° 
121.1° 
124.0° 
120.4° 
120.0° 
122.5° 
123.4° j 
120. 9°l 


ence. 


12.6= 
13.7° 
14.0° 
14.4° 
13.3° 
13.7° 
13.3° 
14.1° 
13.0° 
13.7° 
14.2° 
15.1° 
12.4° 


Wet. 


95.2 
96.1° 
97.3° 
97.7° 
98.2° 
99.1° 
99.1° 
99.3° 
99.3° 
99.5° 
99.5° 
101.8° 
103.6° 


Dry. 


108.7° 
109.4° 
110.5° 
111.7° 
111.4° 
112.6° 
112.1° 
112.1° 
112.3° 
113.0° 
113.5° 
115.3° 
117.3° 


Differ- 
ence. 


13.5° 
13.3° 
13.2° 
14.0° 
13.2° 
13.5° 
13.0° 
12.8° 
13.0° 
13.5" 
14.0° 
13.5° 
13.7° 


We  note  that  the  difference  in  favor  of  the  dry  earth  is 
almost  uniformly  13°  to  14°.  This  difference  is  the  same 
as  observed  between  the  whitened  and  blackened  speci- 
mens of  the  same  soils.     (Column  3.) 

We  observe,  however,  that  the  wet  soil  m  no  case  be- 
comes as  warm  as  the  same  soil  whitened.  We  notice 
further  that  of  the  wet  soils,  the  dark-colored  ones,  liumus 
and  marl,  are  most  highly  heated.  Further  it  is  seen  that 
coarse  lime  sand  (carbonate  of  lime)  acquires  3°  higher 
temperature  than  fine  carbonate  of  lime,  both  wet,  prob- 
ably because  evaporation  proceeded  more  slowly  from  the 
coarse  than  from  the  fine  materials.  Again  it  is  plain  on 
comparing  columns  1,  2,  and  5,  that  the  gray  to  yellowish 
brown  and  black  colors  of  all  the  soils,  save  the  first  three, 
assist  the  elevation   of   temperature,  which  rises  nearly 


RELATIONS    OF   THE    SOIL   TO    HEAT.  197 

with  the  deepening  of  the  color,  until  in  case  of  humus  it 
lacks  but  a  few  degrees  of  reaching  the  warmth  of  a  sur- 
face of  lamp-black. 

According  to  the  observations  of  Dickinson,  made  at 
Abbot's  Hill,  Hertfordshire,  England,  and  continued 
through  eight  years,  90  per  cent  of  the  water  falling  be- 
tween April  1st  and  October  1st  evaporates  from  the  sur- 
face of  the  soil,  only  10  per  cent  finding  its  way  into 
drains  laid  three  and  four  feet  deep.  The  total  quantity 
of  water  that  fell  during  this  time  amounted  to  about 
2,900,000  lbs.  per  acre;  of  this  more  than  2,600,000  evap- 
orated from  the  surface.  It  has  been  calculated  that  to 
evaporate  artificially  this  enormous  mass  of  water,  more 
than  seventy-five  tons  of  coal  must  be  consumed. 

Thorough  draining,  by  loosening  the  soil  and  causing  a 
rapid  removal  from  below  of  the  surplus  water,  has  a  most 
decided  influence,  especially  in  spring  time,  in  warming 
the  soil  and  bringing  it  into  a  suitable  condition  for  the 
support  of  vegetation. 

It  is  plain,  then,  that  even  if  we  knew  with  accuracy 
what  are  the  physical  characters  of  a  surface  soil,  and  if 
we  were  able  to  estimate  correctly  the  influence  of  these 
characters  on  its  fertility,  still  we  must  investigate  those 
circumstances  which  affect  its  wetness  or  dryness,  whether 
they  be  an  impervious  subsoil,  or  springs  coming  to  the 
surface,  or  the  amount  and  frequency  of  rain-falls,  taken 
in  connection  with  other  meteorological  causes.  We  can- 
not decide  that  a  clay  is  too  wet  or  a  sand  too  dry,  until 
we  know  its  situation  and  the  climate  it  is  subjected  to. 

The  great  deserts  of  the  globe  do  not  owe  their, barren- 
ness to  necessary  poverty  of  soil,  but  to  meteorological 
influences — to  the  continued  prevalence  of  parching  winds, 
and  the  absence  of  mountains,  to  condense  the  atmospheric 
water  and  establish  a  system  of  rivers  and  streams.  This 
is  not  the  place  to  enter  into  a  discussion  of  the  causes 
that  may  determine  or  modify  climate ;  but  t  o  illustrate 


198  HOW    CROPS   PEED. 

the  effect  that  may  be  produced  by  means  within  human 
control,  it  may  be  stated  that  previous  to  the  year  1821, 
the  French  district  Proveuce  was  a  fertile  and  well-water- 
ed region.  In  1822,  the  olive  trees  which  were  largely 
cultivated  there  v\^ere  injured  by  frost,  and  the  inhabitants 
began  to  cut  them  up  root  and  branch.  This  amounted 
to  clearing  off  a  forest,,  and,  in  consequence,  the  streams 
dried  up,  and  the  productiveness  of  the  country  was  seri- 
ously diminished. 

The  Angle  at  wMcli  tlie  Siia's  Rays  Strike  a  Soil  is 
of  great  mfluence  on  its  temperature.  The  more  this  ap- 
proaches a  right  angle  the  greater  the  heating  effect.  In 
the  latitude  of  England  the  sun's  heat  acts  most  power- 
fully on  surfaces  having  a  southern  exposure,  and  which 
are  inclined  at  an  angle  of  25°  and  30°.  The  best  vine- 
yards of  the  Rhine  and  ISTeckar  are  also  on  hill-sides,  so 
situated.  In  Lapland  and  Spitzbergen  the  southern 
side  of  hills  may  be  seen  covered  with  vegetation,  while 
lasting  or  even  perpetual  snow  lies  on  their  northern  in- 
clinations. 

The  Infiueace  of  a  Wall  or  other  Eeflectmg  Surface 

upon  the  warmth  of  a  soil  lying  to  the  south  of  it  was 
observed  in  the  case  of  garden  soil  by  Malaguti  and 
Durocher.  The  highest  temperature  indicated  by  a  ther- 
mometer placed  in  this  soil  at  a  distance  of  six  inches  from 
the  wall,  during  a  series  of  observations  lasting  seven  days 
(April,  1852),  was  32°  Fahrenheit  higher  at  the  surface, 
and  18°  higher  at  a  depth  of  four  inches  than  in  the  same 
soil  on  the  north  side  of  the  wall.  The  average  temper- 
ature of  the  former  during  this  time  was  8°  higher  than 
that  of  the  latter.  In  another  trial  in  March  the  difference 
in  average  temperature  between  the  southern  and  north- 
ern exposures  was  nearly  double  this  amount  in  favor  of 
the  former. 

As  is  well  known,  fruits  which  refuse  to  ripen  in  cold 
climates  under  ordinary  conditions  of  exposure  may  attain 


THE   FREE    WATER    OF    THE    SOIL.  199 

perfection  when  trained  against  the  sunny  side  of  a  wall. 
It  is  thus  that  in  the  north  of  England  pears  and  plums 
are  raised  in  the  most  unfavorable  seasons,  and  that  the 
vineyards  of  Fontainebleau  produce  such  delicious  Chas- 
selas  grapes  for  the  Paris  market,  the  vines  being  trained 
against  walls  on  the  Thomery  system. 

In  the  Rhine  district  grape  vines  are  kept  low  and  as 
near  the  soil  as  possible,  so  that  the  heat  of  the  sun  may  be 
reflected  back  upon  them  from  the  ground,  and  the  ripen- 
ing is  then  carried  through  the  nights  by  the  heat  radiated 
from  the  earth. — {Journal  Highland  and  Agricidtural 
Society,  July,  1858,  p.  347.) 

Vegetation. — Malaguti  and  Durocher  also  studied  the 
effect  of  a  sod-  on  the  temperature  of  the  soil.  They  ob- 
served that  it  hindered  the  warming  of  the  soil,  and  in- 
deed to  about  the  same  extent  as  a  layer  of  earth  of  three 
inches  depth.  Thus  a  thermometer  four  inches  deep  in 
green-sward  acquires  the  same  temperature  as  one  seven 
inches  deep  in  the  same  soil  not  grassed. 


CHAPTER     V. 

THE    SOIL    AS    A    SOURCE    OF    FOOD    TO    CROPS.— 

INGREDIENTS    WHOSE    ELEMENTS    ARE    OF 

ATMOSPHERIC    ORIGIN. 

§  1- 

THE  FREE  WATER  OF  THE  SOIL  IN  ITS  RELATIONS  TO 
VEGETABLE  NUTRITION. 

Water  may  exist  free  in  the  soil  in  three  conditions, 
which  we  designate  respectively  hydrostatic,  capillary, 
and  hygroscopic. 

Hydrostatic  ©r  Flowing*  Water  is  water  visible  as 


*  I.  e,,  capable  of  flowing 


200  now  CHOPS  feed. 

such  to  the  eye,  and  free  to  obey  the  laws  of  gravity  and 
motion.  When  the  soil  is  saturated  by  rains,  melting 
snows,  or  by  overflow  of  streams,  its  pores  contain  hy- 
drostatic water,  which  sooner  or  later  sinks  away  into  the 
subsoil  or  escapes  into  drains,  streams,  or  lower  situations. 

Bottom  Water  is  jpermanent  hydrostatic  water ^  reached 
nearly  always  in  excavating  deep  soils.  The  surface  of 
water  in  a  well  corresponds  with,  or  is  somewhat  below,  the 
upper  limit  of  bottom  water.  It  usually  fluctuates  in 
level,  rising  nearer  the  surface  of  the  soil  in  wet  seasons, 
and  receding  during  drought.  In  general,  agricultural 
plants  are  injured  if  their  roots  be  immersed  for  any  length 
of  time  in  hydrostatic  water ;  and  soils  in  which  bottom 
water  is  found  at  a  little  depth  during  the  season  of 
growth  are  unprofitable  for  culture. 

If  this  depth  be  but  a  few  inches,  we  have  a  bog, 
swamp,  or  swale.  If  it  is  one  and  a  half  to  three  feet, 
and  the  surface  soil  be  light,  gravelly,  or  open,  so  as  to 
admit  of  rapid  evaporation,  some  plants,  especially  grasses, 
may  flourish.  If  at  a  constant  depth  of  four  to  eight  feet 
under  a  gravelly  or  light  loamy  soil,  it  is  favorable  to 
crops  as  an  abundant  source  of  water. 

Heavy  clays,  which  retain  hydrostatic  water  for  a  long 
time,  being  but  little  permeable,  are  for  the  same  reasons 
unfavorable  to  most  crops,  unless  artificial  provision  be 
made  for  removing  the  excess. 

Rice,  as  we  have  seen,  (H.  C.  G.,  p.  252),  is  a  plant 
which  grows  well  with  its  roots  situated  in  water.  Hen- 
rici's  experiment  with  the  raspberry  (H.  C.  G.,  p.  254), 
and  the  frequent  finding  of  roots  of  clover,  turnips,  etc., 
in  cisterns  or  drain  pipes,  indicate  that  many  or  all 
agricultural  plants  may  send  down  roots  into  the  bottom 
water  for  the  purpose  of  gathering  a  sufficient  supply  of 
this  necessary  liquid. 

Capillary  Water  is  that  which  is  held  in  the  fine  pores 
of  the  soil  by  the  surface  attraction  of  its  particles,  as  oil 


THE    FEEE    WATER    OF   THE    SOIL.  201 

is  held  in  the  wick  of  a  lamp.  The  adhesion  of  the  water 
to  the  particles  of  earth  suspends  the  flow  of  the  liquid, 
and  it  is  no  longer  subject  to  the  laws  of  hydrostatics. 
Capillary  water  is  usually  designated  as  moisture^  though 
a  soil  saturated  with  capillary  water  would  be,  in  most 
cases,  wet.  The  capillary  power  of  various  soils  has  al- 
ready been  noticed,  and  is  for  coarse  sands  25''|g;  for 
loams  and  clays,  40  to  70°  \^ ;  for  garden  mould  and  humus, 
much  higher,  90  to  300  °  |„.     (See  p.  180.) 

For  a  certain  distance  above  bottom  water,  the  soil  is 
saturated  with  capillary  water,  and  this  distance  is  the 
greater,  the  greater  the  capillary  power  of  the  soil,  i.  e., 
the  finer  its  pores. 

Capillary  water  is  not  visible  as  a  distinct  liquid  layer 
on  or  between  the  particles  of  soil,  but  is  still  recogniza- 
ble by  the  eye.  Even  in  the  driest  weather  and  in  the 
driest  sand  (that  is,  when  not  shut  off  from  bottom  water 
by  too  great  distance  or  an  intervening  gravelly  subsoil)  it 
may  be  found  one  or  a  few  inches  below  the  surface  where 
the  soil  looks  moist — has  a  darker  shade  of  color. 

Hydroscopic  Water  is  that  which  is  not  perceptible  to 
the  senses,  but  is  appreciated  by  loss  or  gain  of  weight  in 
the  body  which  acquires  or  is  deprived  of  it.  (H.  C.  G., 
p.  54.)  The  loss  experienced  by  an  air-dry  soil  when  kept 
for  some  hours  at,  or  slightly  above,  the  boiling  point 
(212°  F.,)  expresses  its  content  of  hygroscopic  water. 
This  quantity  is  variable  according  to  the  character  of  the 
soil,  and  is  constantly  varying  with  the  temperature ;  in- 
creasing during  the  night  when  it  is  collected  from  the  at- 
mosphere, and  diminishing  during  the  day  when  it  returns 
in  part  to  the  air.  (See  p.  164.)  The  amount  of  hygros- 
copic water  ranges  from  0.5  to  10  or  more  per  cent. 

Value  of  these  Distinctions. — These  distinctions  be- 
tween hydrostatic,  capillary,  and  hygroscopic  water,  are 
nothing  absolute,  but  rather  those  of  degree.  Hygroscopic 
water  is  capillary  in  all  respects,  save  that  its  quantity  is 


202  HOW    CROPS    FEED. 

small,  and  its  adhesion  to  the  particles  of  soil  more  firm 
for  that  reason.  Again,  no  precise  boundary  can  always 
be  drawn  between  capillary  and  hydrostatic  water,  espe- 
cially in  soil  having  fine  pores.  The  terms  are  neverthe- 
less useful  in  conveying  an  idea  of  the  degrees  of  wet- 
ness or  moisture  in  the  soil. 

Roots  Absorl)  Capillary  or  Hygroscopic  Water, — It  is 
from  capillary  or  hygroscopic  water  that  the  roots  of  most 
agricultural  plants  chiefly  draw  a  supply  of  this  liquid, 
though  not  infrequently  they  send  roots  into  wells  and 
drains.  The  physical  characters  of  soils  that  have  been 
already  considered  sufiice  to  explain  how  the  earth  acquires 
this  water ;  it  here  remains  to  notice  how  the  plant  is  re- 
lated to  it. 

As  we  have  seen  (pp.  35-38),  the  aerial  organs  appear 
incapable  of  taking  up  either  vapor  or  liquid  water  from 
the  air  to  much  extent,  and  even  roots  continually  exhale 
vapor  without  absorbing  any,  or  at  least  without  being  able 
to  make  up  the  loss  which  they  continually  sufi'er. 

Transpiration  of  Water  tlirongh  Plants. — It  is  a  most 
familiar  fact  that  water  constantly  exhales  from  the  surface 
of  the  plant.  The  amount  of  this  exhalation  is  often  very 
great.  Hales,  the  earliest  observer  of  this  phenomenon, 
found  that  a  sunflower  whose  foliage  had  39  square  feet 
of  surface,  gave  off  in  24  hours  3  lbs.  of  water.  A  cab- 
bage, whose  surface  of  leaves  equaled  19  square  feet,  ex- 
haled in  the  same  time  very  nearly  as  much.  Schleiden 
found  the  loss  of  water  from  a  square  foot  of  grass-sod  to 
be  more  than  \\  lbs.  in  24  hours.  Schubler  states  that  in 
the  same  time  1  square  foot  of  pasture-grass  exhaled 
nearly  5J  lbs.  of  water.  In  one  of  Knop's  more  recent 
experiments,  {Ys.  jSt.,  VI,  239),  a  dwarf  bean  exhaled 
during  23  days,  in  September  and  October,  13  times  its 
weight  of  water.  In  another  trial  a  maize-plant  transpir- 
ed 36  times  its  weight  of  water,  from  May  22d  to  Sept. 
4th.     According  to  Knop,  a  grass-plant  will  exhale  its  own 


THE    FREE   WATER    OP   THE    SOIL.  203 

weight  of  water  in  24  hours  of  hot  and  dry  summer 
weather. 

The  water  exhaled  from  the  leaves  must  be  constantly 
supplied  by  absorption  at  the  roots,  else  the  foliage  soon 
becomes  flabby  or  wilts,  and  finally  dies.  Except  so  far 
as  water  is  actually  formed  or  fixed  within  the  plant,  its 
absorption  at  the  roots,  its  passage  through  the  tissues, 
and  its  exhalation  from  the  foliage,  are  nearly  equal  in 
quantity  and  mutually  dependent  during  the  healthy  ex- 
istence of  vegetation. 

Circumstances  that  Influesce  Transpiration.— c^  The 

structure  of  the  leaf  including  the  character  of  the  epi- 
dermis, and  the  number  of  stomata  as  they  affect  exhala- 
tion, has  been  considered  in  "  How  Crops  Grow,"  (pp. 
286-8). 

h.  The  physical  conditions  which  facilitate  evapora- 
tion increase  the  amount  of  water  that  passes  through 
the  plant.  Exhalation  of  water-vapor  proceeds  most 
rapidly  in  a  hot,  dry,  windy  summer  day.  It  is  nearly 
checked  when  the  air  is  saturated  with  moisture,  and  va- 
ries through  a  wide  range  according  to  the  conditions  just 
named. 

c.  The  oxidations  that  are  constantly  going  on  toithin 
the  plant  may,  under  certain  conditions,  acquire  sufficient 
intensity  to  develop  a  perceptible  amount  of  heat  and 
cause  the  vaporization  of  water.  It  has  been  repeatedly 
noticed  that  the  process  of  flowering  is  accompanied  by 
considerable  elevation  of  temperature,  (p.  24).  In  general, 
however,  the  opposite  process  of  deoxidation  preponder- 
ates with  the  plant,  and  this  must  occasion  a  reduction  of 
temperature.  These  interior  changes  can  have  no  a|)precia- 
ble  influence  upon  transpiration  as  compared  with  those 
that  ^lepend  upon  external  causes.  Sachs  found  in  some 
of  his  experiments  (p.  36)  that  exhalation  took  place  from 
plants  confined  in  a  limited  space  over  water.     Sachs  be- 


204  HOW    CROPS    FEED. 

lieved  that  the  air  surroundmg  the  plants  in  these  experi- 
ments was  saturated  with  vapor  of  water,  and  concluded 
that  heat  was  developed  within  the  plant,  which  caused 
vaporization.  More  recently,  Boehm  [Sltzungsherichte 
der  Wiener  Akad.^  XLYIII,  15)  has  made  probable  that 
the  air  was  not  fully  or  constantly  saturated  with  moist- 
ure in  these  experiments,  and  by  taking  greater  precau- 
tions has  arrived  at  the  conclusion  that  transpiration  abso- 
lutely ceases  in  air  saturated  with  aqueous  vapor. 

d.  The  condition  of  the  tissues  of  the  plant,  as  depend- 
ent upon  their  age  and  vegetative  activity,  likewise  has  a 
marked  effect  on  transpiration.  Lawes  *  and  Knop  both 
found  that  young  plants  lose  more  water  than  older  ones. 
This  is  due  to  the  diminished  power  of  mature  foliage  to 
imbibe  and  contain  water,  its  cells  becoming  choked  up 
with  growth  and  inactive. 

e.  The  character  of  the  medium  in  which  the  roots  are 
situated  also  remarkably  influences  the  rate  of  transpira- 
tion. This  fact,  first  observed  by  Mr.  Lawes,  in  1850,  loc. 
cit.,  was  more  distinctly  brought  out  by  Dr.  Sachs  at  a 
later  period.     ( Vs.  jSt.,  I,  p.  203.) 

Sachs  experimented  on  various  plants,  viz. :  beans, 
squashes,  tobacco,  and  maize,  and  observed  their  transpi- 
ration in  weak  solutions  (mostly  containing  one  per  cent) 
of  nitre,  common  salt,  gypsum,  (one-fifth  per  cent  solu- 
tion) and  sulphate  of  ammonia.  He  also  experimented 
with  maize  in  a  mixed  solution  of  phosphate  and  silicate 
of  potash,  sulphates  of  lime  and  magnesia,  and  common 
salt,  and  likewise  observed  the  effect  of  free  nitric  acid 
and  free  potash  on  the  squash  plant.  The  young  plants 
were  either  germinated  in  the  soil,  then  removed  from  it 
and  set  with  their  rootlets  in  the  solution,  or  else  were 
kept  in  the  soil  and  watered  with  the  solution.     The  glass 


*  Experimental  Investigation  into   the  Amount  of  Water  given  off  by  Plants 
during  their  Groivth,  by  J.  B.  Lawes,  of  Rothamstead,  Loudon,  1850. 


THE    FKEE    WATER    OF   THE    SOIL.  205 

vessel  containing  the  plant  and  solution  was  closed  above, 
around  the  stem  of  the  plant,  by  glass  plates  and  cement, 
so  that  no  loss  of  water  could  occur  except  through  the 
plant  itself,  and  this  loss  was  ascertained  by  daily  weigh- 
ings. The  result  was  that  all  the  solutions  mentioned, 
excej^t  that  of  free  nitric  acid,  quite  uniformly  retarded 
transpiration  to  a  degree  varying  from  10  to  90  per  cent, 
while  the  free  acid  accelerated  the  transpiration  in  a  cor- 
responding manner. 

Sachs  experimented  also  with  four  tobacco  plants,  two 
situated  in  coarse  sand  and  two  in  yellow  loam.  The 
plants  stood  side  by  side  exposed  to  the  same  temperature, 
etc.,  and  daily  weighings  were  made  during  a  week  or 
more,  to  learn  the  amount  of  exhalation.  The  result  was 
that  the  total  loss,  as  well  as  the  daily  loss  in  the  majority 
of  weighings,  was  greater  from  the  plant  growing  in  loam, 
although  through  certain  short  periods  the  opposite  was 
noticed. 

f.  The  temperature  of  the  soil  considerably  affects  the 
rate  of  transpiration  by  influencing  the  amount  of  absorp- 
tion at  the  roots.  Sachs  made  a  number  of  weighings  up- 
on two  tobacco  j)lants  of  equal  size,  potted  in  portions  of 
the  same  soil  and  having  their  foliage  exposed  to  the  same 
atmosphere.  After  observing  their  relative  transpiration 
when  their  roots  were  at  the  same  temperature,  one  pot 
was  warmed  a  number  of  degrees,  and  the  result  was  in- 
variably observed  that  elevating  the  temperature  of  the 
soil  increased  the  transpiration. 

The  same  observer  subsequently  noticed  the  entire  sup- 
jpression  of  absorption  by  a  reduction  of  temperature  to 
41°  to  43°  F.  A  number  of  healthy  tobacco  and  squash 
plants,  rooted  in  a  soil  kept  nearly  saturated  with  water, 
were  growing  late  in  ^N'ovember  in  a  room,  the  tempera- 
ture of  which  fell  at  night  to  the  point  just  named.  In 
the  morning  the  leaves  of  these  plants  were  so  wilted 
that  they  hung  down  like  wet  cloths,  as  if  the  soil  were 


306  HOW    CEOPS    FEED. 

completely  dry,  or  they  liad  been  for  a  long  time  acted 
upon  ]:y  a  powerful  sun.  Since,  however,  the  soil  was 
moist,  the  wilting  could  only  arise  from  the  inability  of 
the  roots  to  absorb  water  as  rapidly  as  it  exhaled  from 
the  leaves,  owing  to  the  Ioav  temperature.  Further  ex- 
periments showed  that  warming  the  soil  in  which  the 
wilted  plants  stood,  restored  the  foliage  to  its  proper  tur- 
gidity  in  a  short  time,  and  by  surrounding  the  soil  of  a 
fresh  plant  Yvdth  snow,  the  leaves  wilted  in  three  or  four 
hours. 

Cabbages,  winter  colza,  and  beans,  similarly  circum- 
stanced, did  not  wilt,  showing  that  different  plants  are  un- 
equally aifected.  The  general  rule  nevertheless  appears  to 
be  established  that  within  certain  limits  the  root  absorbs 
more  vigorously  at  high  than  at  low  temperatures. 

Tlie  AM^uiit  of  Loss  of  Water  ©f  Vegetation  in  Wilt- 
ing" has  been  determined  by  Hesse  ( Vs.  j8l,  I,  248)  in 
case  of  sugar-beet  leaves.  Of  two  similar  leaves,  one, 
gathered  at  evening  after  several  days  of  dryness  and  sun- 
shine, contained  85.74° |^  of  water;  the  other,  gathered 
the  next  morning,  two  hours  after  a  rain  storm,  yielded 
89.57°!,.  The  difference  was  accordingly  3.8°  |„.  Other 
observations  corroborated  this  result. 

Is  Exhalation  Indispensable  to  Plants  ] — It  was  for 

a  long  time  supposed  that  transpiration  is  indispensable 
to  the  life  of  plants.  It  was  taught  that  the  water  which 
the  i^lant  imbibes  from  the  soil  to  replace  that  lost  by  ex- 
halation, is  the  means  of  bringing  into  its  roots  the  min- 
eral and  other  soluble  substances  that  serve  for  its  nutri- 
ment. 

There  are,  however,  strong  grounds  for  believing  that 
the  current  of  water  which  ascends  through  a  plant  moves 
independently  of  the  matters  that  may  be  in  solution, 
either  without  or  within  it ;  and,  moreover,  the  motion  of 
soluble  matters  from  the  soil  into  the  plant  may  go  on, 


THE    FEEH    WATER    OF    THE    SOIL.  207 

although,  there  be  no  ascending  aqueous  current.     (H.  C. 
G.,  pp.  288  and  340.) 

In  accordance  with  these  views,  vegetation  grows  as  well 
in  the  confined  atmosphere  of  green-houses  or  of  Wardian 
Cases,  where  the  air  is  for  the  most  part  or  entirely  satu- 
rated with  vapor,  so  that  transpiration  is  reduced  to  a  mini- 
mum, as  in  the  free  air,  where  it  may  attain  a  maximum. 
As  is  well  known,  the  growth  of  field  crops  and  garden 
vegetables  is  often  most  rapid  during  damp  and  showery 
weather,  when  the  transpiration  must  proceed  with  com- 
parative slowness. 

While  the  above  considerations,  together  with  the  asser- 
tion of  Knop,  that  leaves  lose  for  the  first  half  hour  nearly 
the  same  quantities  of  water  under  similar  exposure, 
whether  they  are  attached  to  the  stem  or  removed  from 
it,  whether  entire  or  in  fragments,  would  lead  to  the  con- 
clusion that  transpiration,  which  is  so  extremely  variable 
in  its  amount,  is,  so  to  speak,  an  accident  to  the  plant  and 
not  a  process  essential  to  its  existence  or  welfare,  there 
are,  on  the  other  hand,  facts  which  appear  to  indicate  the 
contrary. 

In  certain  experiments  of  Sachs,  in  which  the  roots  of 
a  bean  were  situated  m  an  atmosphere  nearly  saturated 
with  aqueous  vapor,  the  foliage  being  exposed  to  the  air, 
although  the  plant  continued  for  two  months  fresh  and 
healthy  to  appearance,  it  remained  entirely  stationary  in 
its  development.     ( Vs.  jSt,  I,  237.) 

Knop  also  mentions  incidentally  ( Vs.  /St.,  I,  192)  that 
beans,  lupines,  and  maize,  die  when  the  whole  plant  is 
kept  confined  in  a  vessel  over  water. 

It  is  not,  however,  improbable  that  the  cessation  of 
growth  in  the  one  case  and  the  death  of  the  j)lants  in  the 
other  were  due  not  so  much  to  the  checking  of  transpira- 
tion, -which,  as  we  have  seen,  is  never  entirely  suppressed 
under  these  circumstances,  as  to  the  exhaustion  of  oxygen 
or  the  undue  accumulation  of  carbonic  acid  in  the  narrow 


208  HOW   CROPS   FEED. 

and  confined  atmosphere  in  which  these  results  were 
noticed. 

On  the  whole,  then,  we  conclude  from  the  evidence  be- 
fore us  that  transpiration  is  not  necessary  to  vegetation, 
or  at  least  fulfills  no  very  important  ofiices  in  the  nutrition 
of  plants. 

The  entrance  of  water  into  the  plant  and  the  steady 
maintenance  of  its  proper  content  of  this  substance,  under 
all  circumstances  is  of  the  utmost  moment,  and  leads  us 
to  notice  in  the  next  place  the 

Direct  Proof  that  Crops  can  Absorl)  from  the  Soil 
enough  Hygroscopic  Water  to  Maintain  their  Life.— Sachs 
suffered  a  young  bean-plant  standing  in  a  pot  of  very  reten- 
tive (clay)  soil  to  remain  without  watering  until  the  leaves 
began  to  wilt.  A  high  and  spacious  glass  cylinder,  having 
a  layer  of  water  at  its  bottom,  was  then  provided,  and  the 
pot  containing  the  wilting  plant  was  supported  in  it,  near 
its  top,  while  the  cylinder  was  capped  by  two  semicircular 
jilates  of  glass  which  closed  snugly  about  the  stem  of  the 
bean.  The  pot  of  soil  and  the  roots  of  the  plant  were 
thus  enclosed  in  an  atmosphere  which  was  constantly  sat- 
urated, or  nearly  so,  with  watery  vapor,  while  the  leaves 
were  fully  exposed  to  the  free  air.  It  was  now  to  be  ob- 
served whether  the  water  that  exhaled  from  the  leaves 
could  be  supplied  by  the  hygroscopic  moisture  which  the 
soil  should  gather  from  the  damp  air  enveloping  it.  This 
j)roved  to  be  the  case.  The  leaves,  previously  wilted,  re- 
covered their  proper  turgidity,  and  remained  fresh  during 
the  two  months  of  June  and  Jidy. 

Sachs,  having  shown  in  other  experiments  that  plants 
situated  precisely  like  this  bean,  save  that  the  roots  are  not 
in  contact  with  soil,  lose  water  continuously  and  have  no 
power  to  recover  it  from  damp  air  (p.  86)  thus  gives  us 
demonstration  that  the  clay  soil  which  condenses  vapor  in 
its  pores  and  holds  it  as  hygroscopic  water,  yields  it  again 
to  the  plant,  and  thus  becomes  the  medium  through  which 


THE    FEEE    WATER    OF    THE    SOIL.  209 

water  is   continually   carried   from  the   atmosphere  into 
vegetation. 

In  a  similar  experiment,  a  tobacco  plant  was  employed 
which  stood  in  a  soil  of  humus.  This  material  was  also 
capable  of  supplying  the  plant  with  water  by  virtue  of 
its  hygroscopic  i)ower,  but  less  satisfactorily  than  the  clay. 
As  already  mentioned,  these  plants,  while  remaining  fresh, 
exhibited  no  signs  of  growth.  This  may  be  due  to  the 
consumption  of  oxygen  by  the  roots  and  soil,  or  possibly 
the  roots  of  plants  may  require  an  occasional  drenching 
with  liquid  water.  Further  investigations  in  this  direc- 
tion are  required  and  promise  most  interesting  results. 

What  Proportion  of  the  Capillary  and  Hygroscopic 
Water  of  the  Soil  may  Plants  Absorb,  is  a  question  that 
Dr.  Sachs  has  made  the  only  attempts  to  answer.  When 
a  plant,  whose  leaves  are  in  a  very  moist  atmosphere,  wilts 
or  begins  to  wilt  in  the  night  time,  when  therefore  trans- 
piration is  reduced  to  a  minimum,  it  is  because  the  soil  no 
longer  yields  it  water.  The  quantity  of  water  still  con- 
tained in  a  soil  at  that  juncture  is  that  which  the  plant 
cannot  remove  from  it, — is  that  which  is  unavailable  to 
vegetation,  or  at  least  to  the  kind  of  vegetation  experi- 
mented with.  Sachs  made  trials  on  this  principle  with 
tobacco  plants  in  three  different  soils. 

The  plant  began  to  wilt  in  a  mixture  of  hlach  humus 
(from  beech-wood)  and  sanely  when  the  soil  contained 
12.3°  Iq  of  water.*  This  soil,  however,  was  capable  of 
holding  46°  |g  of  capillary  water.  It  results  therefore  that 
of  its  highest  content  of  absorbed  water  33.7°  |„  (=46-12.3) 
Avas  available  to  the  tobacco  plant. 

Another  plant  began  to  wilt  on  a  rainy  night,  while  the 
loam  it  stood  in  contained  8°|\,  of  water.  This  soil  was 
able  to  absorb  52.1°|  ^  of  water,  so  that  it  might    after 


Ascertained  by  drying  at  212°. 


210  HOW    CROPS    FEED. 

saturation,  furnish  the  tobacco  plant  with  44.1°  |g  of  its 
weight  of  water. 

A  coarse  sand  that  could  hold  20.8°  j„  of  water  was 
found  to  yield  all  but  1.5°  |g  to  a  tobacco  plant. 

From  these  trials  we  gather  with  at  least  approximate 
accuracy  the  power  of  the  plant  to  extract  water  from 
these  several  soils,  and  by  difference,  the  quantity  of  wa- 
ter in  them  that  was  unavailable  to  the  tobacco  plant. 

Sow  do  tlie  Roots  take  Hygroscopic  Water  from  the 
§©!!  ] — The  entire  plant,  when  living,  is  itself  extremely 
hygroscopic.  Even  the  dead  plant  retains  a  certain  pro- 
portion of  Avater  with  great  obstinacy.  Thus  wheat, 
maize,  starch,  straw,  and  most  air-dry  vegetable  substances, 
contain  12  to  15°  1^^  of  water;  and  when  these  matters  are 
exposed  to  damp  air,  they  can  take  up  much  more.  Ac- 
cording to  Trommer  {JBodenkunde^  p.  270),  100  parts  of 
the  following  matters,  when  dry,  absorb  from  moist  air  in 

13   24   48   72 


Ine  cut  Laiiey  straw, 
"      "    rye 

15 
12 

hours. 
24      ai 

20        27 

45  parts  of  water, 
29      "      "       " 

"   "  "wbit®  unsized  paper,     8   12   17   19  "   "   " 

As  already  explained,  a  body  is  hygroscopic  because 
there  is  attraction  between  its  particles  and  the  particles 
of  water.  The  form  of  attraction  exerted  thus  among 
different  kinds  of  matter  is  termed  adhesive  attraction,  or 
simply  adhesion. 

Adhesion  acts  only  through  a  small  distance,  but  its  in- 
tensity varies  greatly  within  this  distance.  If  we  attempt 
to  rem.ove  hygroscopic  water  from  starch  or  any  similar 
body  by  drying  at  212°,  v/e  shall  find  that  the  greater 
part  of  the  moisture  is  easily  expelled  in  a  short  time, 
but  we  shall  also  notice  that  it  requires  a  relatively  much 
longer  time  to  expel  the  last  portions.  A  general  law  of 
attraction  is  that  its  force  diminishes  as  the  distance  be- 
tween the  attractino:  bodies  increases.     This  has  been  ex- 


THE    FKEE    AYATEK    OF    THE    SOIL.  211 

actly  demonstrated  in  case  of  the  force  of  gravity  and 
electrical  attraction,  which  act  through  great  intervals  of 
space. 

We  must  therefore  suppose  that  when  a  mass  of  hygro- 
scopic matter  is  allowed  to  coat  itself  with  water  by  the 
exercise  of  its  adhesive  attraction,  the  layer  of  aqueous 
particles  which  is  in  nearest  contact  is  more  strongly  held 
to  it  than  the  next  outer  layer,  and  the  adhesion  diminish- 
es with  the  distance,  until,  at  a  certain  point,  still  too 
small  for  us  to  jDcrceive,  the  attraction  is  nothing,  or  is 
neutralized  by  other  opposing  forces,  and  further  adhesion 
ceases. 

Supj^ose,  now,  we  bring  in  contact  at  a  single  point  two 
masses  of  the  same  kind  of  matter,  one  of  which  is  satu- 
rated with  hygroscopic  water  and  the  other  is  perfectly  dry. 
It  is  plain  that  the  outer  layers  of  water-particles  adhering 
to  the  moist  body  come  at  once  within  the  range  of  a 
more  powerful  attraction  exerted  by  the  very  surface  of 
the  dry  body.  The  external  particles  of  water  attached 
to  the  first  must  then  pass  to  the  second,  and  they  must 
also  distribute  themselves  equally  over  the  surface  of  the 
latter ;  and  this  motion  must  go  on  until  the  attraction 
of  the  two  surfaces  is  equally  satisfied,  and  the  water  is 
equally  distributed  according  to  the  surface,  i.  e.,  is  uni- 
form over  the  whole  surface. 

If  of  two  difierent  bodies  put  in  contact  (one  dry  and 
one  moist)  the  surfaces  be  equal,  but  the  attractive  force 
of  one  for  water  be  twice  that  of  the  other,  then  motion 
must  go  on  until  the  one  has  appropriated  two-thirds,  and 
the  other  is  left  with  one-third  the  total  amount  of  water. 

When  bodies  in  contact  have  thus  equalized  the  water 
at  their  disposal,  they  may  be  said  to  be  in  a  condition  of 
hygroscopic  equilibrium.  Any  cause  which  disturbs  this 
equilibrium  at  once  sets  up  motion  of  the  hygroscopic 
water,  which  always  proceeds  from  the  more  dry  to  the 
less  dry  body. 


212  HOW    CiiOPS    FEED. 

The  application  of  these  principles  to  the  question  be- 
fore us  is  apparent.  The  young,  active  roots  that  are  in 
contact  with  the  soil  are  eminently  hygroscopic,  as  is  de- 
monstrated by  the  fact  that  they  supply  the  plant  with 
large  quantities  of  water  when  the  soil  is  so  dry  that  it 
has  no  visible  moisture.  They  therefore  share  with  the 
soil  the  moisture  which  the  latter  contains.  As  water 
evaporates  from  the  surface  of  the  foliage,  its  place  is 
supplied  by  the  adjacent  j^ortions,  and  thus  motion  is  es- 
tablished within  the  plant  which  propagates  itself  to  the 
roots  and  through  these  to  the  soil. 

Each  particle  of  water  that  flies  off  in  vapor  from  the 
leaf  makes  room  for  the  entrance  of  a  particle  at  the  root. 
If  the  soil  and  air  have  a  surplus  of  water,  the  plant  will 
contain  more ;  if  the  soil  and  air  be  dry,  it  will  contain 
less.  Within  certain  narrow  limits  the  supply  and  waste 
may  vary  without  detriment  to  the  plant,  but  when  the 
loss  goes  on  more  rapidly  than  the  supply  can  be  kept  up, 
or  when  the  absolute  content  of  Avater  in  the  soil  is  re- 
duced to  a  certain  point,  the  plant  shortly  wilts.  Even 
then  its  content  of  w^ater  is  many  times  greater  than  that 
of  the  soil.  The  living  tobacco  plant  cannot  contain  less 
than  80°  Iq  of  w^ater,  while  the  soils  in  Sachs'  experiments 
contained  but  12.3°  |g  and  1.5°  1^  respectively.  When  fully 
air-dry,  vegetable  matter  retains  13°  1^  to  15°  |g  of  water, 
while  the  soil  similarly  dry  rarely  contains  more  than 

1-21.- 

The  plant   therefore,  especially  when  living,  is  much 

more  hygroscopic  than  the  soil. 

If  roots  are  so  hygroscopic,  why,  it  may  be  asked,  do 
they  not  directly  absorb  vapor  of  water  from  the  air  of 
the  soil  ?  It  cannot  be  denied  that  both  the  roots  and  fo- 
liage of  plants  are  capable  of  this  kind  of  absorption, 
and  that  it  is  taking  place  constantly  in  case  of  the  roots. 
The  experiments  before  described  prove,  however,  that 
the  higher  orders  of  plants  absorb  very  little  in  this  way, 


THE    FEEE    WATER    OF    THE    SOIL.  213 

too  little,  in  fact,  to  be  estimated  by  tlie  metbods  bitberto 
employed.  Sacbs  explains  tbis  as  follows :  Assuming  tbat 
tbe  roots  bave  at  a  given  temperature  as  strong  an  attrac- 
tion for  water  in  tbe  state  of  vapor  as  for  liquid  water,  tbe 
amount  of  eacb  taken  up  in  a  given  time  under  tbe  same 
circumstances  would  be  in  proportion  to  tbe  weigbt  of 
eacb  contained  in  a  given  space.  A  cubic  incb  of  water 
yields  at  212°  nearly  a  cubic  foot  (accurately,  1,696  times 
its  volume,  tbe  barometer  standing  at  29.92  incbes)  of 
vapor.  We  may  tben  assume  tbat  tbe  absorption  of  liq- 
uid or  bygroscopic  water  proceeds  at  least  one  tbousand 
times  more  rapidly  tban  tbat  of  vapor,  a  diiference  in 
rate  tbat  enables  us  to  comprebend  wby  a  plant  may  gain 
water  by  its  roots  from  tbe  soil,  wben  it  would  lose  water 
by  its  roots  were  tbey  simply  stationed  in  air  saturated 
witb  vapor. 

Again,  tbe  soil  need  not  be  more  bygroscopic  tban  roots, 
to  supply  tbe  latter  witb  water.  It  is  important  only  tbat 
it  present  a  sufficient  surface.  As  is  well  known,  a  plant 
requires  a  great  volume  of  eartb  to  nourisb  it  properly, 
and  tbe  root-surface  is  trifling,  compared  to  tbe  surface 
of  tbe  particles  wbicb  compose  tbe  soil. 

Boussingault  found  by  actual  measurement  tbat,  accord- 
ing to  tbe  rules  of  garden  culture  as  practiced  near  Stras- 
burg,  a  dwarf  bean  bad  at  its  disposition  57  pounds  of 
soil;  a  potato  plant,  190  pounds;  a  tobacco  plant,  470 
pounds ;  and  a  bop  plant,  2,900  pounds.  Tbese  weigbts 
correspond  to  about  1,  3,  7,  and  50  cubic  feet  respectively. 

The  Quantity  of  Water  in  Vegetation  is  influenced  by 
that  of  the  Soil, — De  Saussure  observed  tbat  plants  grow- 
ing in  a  dry  lime  soil  contained  less  water  tban  tbose  from 
a  loam.  It  is  well  known  tbat  tbe  grass  of  a  wet  summer 
is  taller  and  more  succulent,  and  tbe  green  crop  is  beavier 
tban  tbat  from  tbe  same  field  in  a  dry  summer.  It  does 
not,  bowever,  make  mucb  more  bay,  its  greater  weigbt 
consisting  to  a  large  degree  of  water,  wbicb  is  lost  in  dry^ 


Fresh. 
14,903 
12,380 
22,256 
18,815 

Air-dry. 
5,182 
5,418 
4,800 
5,190 

Water  lost  in  drying. 

9,721 

6,962 
17,456 
13,625 

214  HOW    CROPS    PEED. 

ing.  Ritthausen  gives  some  data  concerning  two  clover 
crops  of  the  year  1854,  from  a  loamy  sand,  portions  of 
which  were  manured,  one  with  ashes,  others  with  gypsum. 
The  following  statement  gives  the  produce  of  the  nearly* 
fresh  and  of  the  air-dry  crops. 

Weight  in  pounds  per  acre. 
Fresh. 
Crop  I,  manured  with  ashes, 

"     "  unmanured, 
Crop  II,  manured  with  gj^psum, 
"    "     unmanured, 

It  is  seen  that  while  in  both  cases  the  fresh  manured 
crop  greatly  outweighed  the  unmanured,  the  excess  of 
weight  consisted  of  vjciter.  In  fact,  the  unmanured  plots 
yielded  more  hay  than  the  manured.  The  manured  clover 
was  darker  in  color  than  the  other,  and  the  stems  were 
large  and  hollow,  i.  e.,  by  rapid  growth  the  pith  cells  were 
broken  away  from  each  other  and  formed  only  a  lining 
to  the  stalk,  while  in  the  unmanured  clover  the  pith  re- 
mained undisturbed,  the  stems  being  more  compact  in 
structure.     (H.  C.  G.,  p.  369.) 

The  Quantity  of  Soil-water  most  favorable  to  Crops 

has  been  studied  by  Ilienkoff  and  Ilellriegel.  The  former 
{Ami.  der.  Ghem.  u.  Ph.  136,  p.  160,)  experimented  with 
buckwheat  plants  stationed  in  pots  filled  with  garden 
earth.  The  pots  were  of  the  same  size  and  had  the  same 
exposure  at  the  south  side  of  an  apartment.  The  plants 
received  at  each  watering:  in 


Pot  Ko. 

1,  '1, 

liter  of  water 

u         a 

2,  "1, 

a 

a 

((            (£ 

3,  '1. 

a 

a 

((        a 

4,  'L. 

a 

u 

u        a 

5,  'L 

a 

a 

*  The  clover  was  collected  from  the  surface  of  a  Saxon  square  ell,  and  was 
somewhat  wilted  before  coming  into  Ritthausen' s  hands.  The  quantities  above 
given  are  calculated  to  English  acres  and  pounds. 


THE   FKEH    WATER    OF    THE    SOIL. 


215 


The  waterings  Y/ere  made  simultaneously  at  the  moment 
when  all  the  water  previously  given  to  l^o.  1  was  ab- 
sorbed by  the  soil.  During  the  67  days  of  the  exjDeri- 
ment  the  plants  were  watered  17  times.  The  subjoined 
table  gives  the  results  : 


Weight  of 

Weight  of 

fresh   Crops    in 

ch^     Crops     in 

Number    of 

Lite7's  of 

JVb.  of  pot. 

grams. 

grams. 

Seeds. 

ivater  used. 

STRAW. 

SEEDS. 

1 

27.99 

4.52 

1.68 

Ill 

25.0 

2 

65.05 

8.47 

5.47 

283 

12.5 

3 

24.95 

4.55 

1.73 

93 

6.25 

4 

9.98 

1.41 

0.52 

87 

3.12 

5 

2.30 

0.30 

0.09 

12 

1.56 

The  experiment  demonstrates  that  the  quantity  of 
water  supplied  to  a  plant  has  a  decided  effect  upon  the 
yield.  Pot  I^o.  2  was  most  favorably  situated  in  this  re- 
spect. ISTo.  1  had  a  surplus  of  water  and  the  other  pots 
received  too  little.  The  experiment  does  not  teach  what 
proportion  of  water  in  the  soil  was  most  advantageous, 
for  neither  the  weight  of  the  soil  nor  the  size  of  the  pot 
is  mentioned. 

Hellriegel  {Ghem.  Ackersmann^  1868,  p.  15)  experiment- 
ed with  wheat,  rye,  and  oats,  in  a  pure  sand  mixed  with  a 
sufficiency  of  plant-food.  The  sand  when  saturated  with 
water  contained  25°  1^  of  the  liquid.  The  following  table 
gives  further  particulars  of  his  experiments  and  the  re- 
sults.    The  weights  are  grams. 


WATER  IN 

THE   SOIL. 

YIELD  01 

WHEAT. 

YIELD   OP  RYE. 

YIELD   OF   OATS. 

In  per  cent 
of  Soil. 

In  per  cent 

of  retentive 

power. 

Straw 
and 
Chaff. 

Grain. 

Straio 
and 
Chaff. 

Cfrain. 

Straw 
and 
Chaff. 

Grain. 

21/2-5 

5    -10 

10    -15 

15    -20 

10-20 
20-40 
40-60 
60-80 

7.0 
15.1 
21.4 
23.3 

2.8 

8.4 

10.3 

11.4 

8.3 
11.8 
15.1 
16.4 

3.9 
8.1 
10.3 
10.3 

4.2  , 
11.8 
13.9 
15.8 

1.8 

7.8 

10.9 

11.8 

In  each  case  the  proportion  of  water  in  the  soil  was 
preserved  within  the  limits  given  in  the  first  column  of 
the  table,  throughout  the  entire  period  of  growth.  It  is 
seen  that  in  this  sandy  soil  10-15  per  cent  of  water  ena- 


216  HOW    CKOPS   FEED. 

bled  rye  to  yield  a  maximum  of  grain  and  brought  wheat 
and  oats  very  closely  to  a  maximum  crojD.  Hellriegel  no- 
ticed that  the  plants  exhibited  no  visible  symptoms  of 
deficiency  of  water,  except  through  stunted  growth,  in 
any  of  these  experiments.  Wilting  never  took  place  ex- 
cept when  the  supply  of  vraterwas  less  than  2'\^  per  cent. 

Grouven  [JJeher  den  Zusammenhang  zwischen  Wit- 
terung^  3oden  tind  Dungung  in  ihrem  EinflusQe  auf  die 
Quantitilt  und  Qualitdt  der  ErndMn^  Glogaii,  1868)  gives 
the  results  of  an  extensive  series  of  field  trials,  in  which, 
among  other  circumstances,  the  influence  of  v^^ater  upon 
the  crops  was  observed.  His  discussion  of  the  subject  is 
too  detailed  to  reproduce  in  this  treatise,  but  the  great 
influence  of  the  supply  of  water  (by  rain,  etc.,)  is  most 
strikingly  brought  out.  The  exi^erimental  fields  were 
situated  in  various  parts  of  Germany  and  Austria,  and 
were  cultivated  with  sugar  beets  in  1862,  under  the  same 
fertilizing  applications,  as  regards  both  kind  and  quantity. 
Of  14  trials  in  which  records  of  the  rain-fall  were  kept, 
the  8  best  crops  received  from  the  time  of  sowing,  May 
1st,  to  that  of  harvesting,  Oct.  15th,  an  average  quantity 
of  rain  equal  to  140  Paris  lines  in  depth.  The  6  poorest 
crops  received  in  the  same  time  on  the  average  but  115 
lines.  During  the  most  critical  period  of  growth,  viz., 
between  the  20th  of  June  and  the  lOtli  of  September,  the 
8  best  crops  enjoyed  an  average  rain-fall  of  90.7  lines, 
while  the  6  poorest  received  but  57.7  lines. 

It  is  a  well  recognized  fact  that  next  to  temperature, 
the  water  supply  is  the  most  influential  factor  in  the  prod- 
uct of  a  crop.  Poor  soils  give  good  crops  in  seasons  of 
plentiful  and  well-distributed  rain  or  when  skillfully  irri- 
gated, but  insufficient  moisture  in  the  soil  is  an  evil  that 
no  supplies  of  j)lant-food  can  neutralize. 

The  Functions  of  Water  in  the  Nourishment  of 
Vegetation,  so  far  as  we  know  them,  are  of  two  kinds. 


THE    FREE    WATER    OF    THE    SOIL.  217 

In  the  first  place  it  is  an  unfailing  and  sufficient  source  of 
its  elements, — hydrogen  and  oxygen, — and  undoubtedly 
enters  directly  or  indirectly  into  chemical  comhination 
with  the  carbon  taken  up  from  carbonic  acid,  to  form  sug- 
ar, starch,  cellulose,  and  other  carbohydrates.  In  the 
second  place  it  performs  important  physical  offices ;  is  the 
vehicle  or  medium  of  all  the  circulation  of  matters  in  the 
plant ;  is  directly  concerned,  it  would  appear,  in  imbibing 
gaseous  food  in  the  foliage  and  solid  nutriment  through 
the  roots ;  and  by  the  force  with  which  it  is  absorbed,  di- 
rectly influences  the  enlargement  of  the  cells,  and,  per- 
haps, also  the  direction  of  their  expansion, — an  effect  shown 
by  the  facts  just  adduced  relative  to  the  clover  crops  ex- 
amined by  Ritthausen. 

Indirectly,  also,  water  performs  the  most  important  ser- 
vice of  continually  solving  and  making  accessible  to  crops 
the  solid  matters  in  the  vicinity  of  their  roots,  as  has 
been  indicated  in  the  chapter  on  the  Origin  of  Soils. 

Combined  Water  ©f  tllC  Soil. — As  already  stated,  there 
may  exist  in  the  soil  compounds  of  which  water  is  a  chemi- 
cal component.  True  clay  (kaolinite)  and  the  zeolites,  as 
well  as  the  oxides  of  iron  that  result  from  weathering,  con- 
tain chemically  combined  water.  Hence  a  soil  which  has 
been  totally  deprived  of  its  hygroscopic  water  by  drying 
at  212°,  may,  and,  unless  consisting  of  pure  sand,  does, 
yield  a  further  small  amount  of  water  by  exposure  to  a 
higher  heat.  This  combined  water  has  no  direct  influence 
on  the  life  of  the  plant  or  on  the  character  of  the  soil,  ex- 
cept so  far  as  it  is  related  to  the  properties  of  the  com- 
pounds of  which  it  is  an  ingredient. 

§2. 
THE  AIR  OF  THE  SOIL. 

As  to  the  free  Oxygen  and  Nitrogen  which  exist  in  the 
interstices  or  adhere  to  the  particles  of  the  soil,  there  is 
10 


218  HOW    CEOPS    FEED. 

little  to  add  here  to  what  has  been  remarked  m  previous 
paragraphs. 

Free  Oxygea,  as  De  Saussure  and  Traube  have  shown, 
is  indispensable  to  growth,  and  must  therefore  be  access- 
ible to  the  roots  of  plants. 

The  soil,  being  eminently  porous,  condenses  oxygen. 
Blumtritt  and  Reichardt  indeed  found  no  considerable 
amount  of  condensed  oxygen  in  most  of  the  soils  and  sub- 
stances they  examined  (p.  167) ;  but  the  experiments  of 
Stenhouse  (p.  169)  and  the  well-known  deodorizing  effects 
of  the  soil  upon  fecal  matters,  leave  no  doubt  as  to  the 
fact.  The  condensed  oxygen  must  usually  spend  itself  in 
chemical  action.  Its  proportion  would  appear  not  to  be 
large ;  but,  being  replaced  as  rapidly  as  it  enters  into  com- 
bination, the  total  quantity  absorbed  may  be  considera- 
ble. Organic  matters  and  lower  oxides  are  thereby  ox- 
idized. Carbon  is  converted  into  carbonic  acid,  hydrogen 
into  water,  protoxide  of  iron  into  peroxide.  The  upper 
portions  of  the  soil  are  constantly  suffering  change  by  the 
action  of  free  oxygen,  so  long  as  any  oxidable  matters 
exist  in  them.  These  oxidations  act  to  solve  the  soil  and 
render  its  elements  available  to  vegetation.     (See  p.  131.) 

Free  Mtrogeu  in  the  air  of  the  soil  is  doubtless  indiffer- 
ent to  vegetation.  The  question  of  its  conversion  into 
nitric  acid  or  ammonia  will  be  noticed  presently.  (See  p. 
259.) 

Carbonic  Acid. — The  air  of  the  soil  is  usually  richer  in 
carbonic  acid,  and  poorer  in  oxygen,  than  the  normal  at- 
mosphere, while  the  proportion  (by  volume)  of  nitrogen 
is  the  same  or  very  nearly  so.  The  proportions  of  car- 
bonic acid  by  weight  in  the  air  included  in  a  variety  of 
soils  have  already  been  stated.  Here  follow  the  total 
quantities  of  this  gas  and  of  air,  as  well  as  the  composi- 
tion of  the  latter  in  100  parts  by  volume,  as  determined  by 


THE    AIR    OF    THE    SOIL. 


219 


Bonssingault  and  Lewy. 
etc.,  p.  369.) 


(Memoires  de  Chhnie  Agricole, 


Sandy  subsoil  of  forest 

Loamy     '•         "      "      

Surface  soil       "      "      

Clayey      "  of  artichoke  field 

Soil  of  asparagus  bed  not  manured  for  one  year 

"    "         ■'  "    newly  manured 

Sandy  soil,  six  days  after  manuring [of  rain 

"  "  ten  ''  "  "  three  days 
Vegetable  mold-compost 


1;   ci 

•s^ 

«^ 

-§f? 

•«.§ 

a  s^ 

.^-# 

«'-' 

b'^ 

b^-i 

Comjmition   of  the 

^  g.g 

air  in  the  soU  in  100 

i 

pm^ts  by  volume. 

Car- 
bonic 

Ox- 

Nitro- 

s^ 

sg 

acid. 

ygen. 

gen. 

4416 

14 

0.24 

3530 

28 

0.79 

19.66 

79.55 

5891 

57 

0.87 

19.61 

79.52 

10310 

71 

0.66 

19.99 

79.35 

11182 

86 

0.74 

19.02 

80.24 

111S2 

172 

1.54 

18.80 

79. 6Q 

11783 

257 

2.21 

11783 

1144 

9.74 

10.35 

79.91 

21049 

772 

3.64 

16.45 

79.91 

§1 

•Is 

os^ 

^Sf^ 

'O.^.S 

•s^ 

"fe^ 

Composition  of  air 

^ 

above  the  soil  in  100 

1.^ 

1  §i 

parts. 

il 

Car- 
bonic 
acid. 

Ox- 
ygen. 

Nitro- 
gen. 

50820 

12 

0.025 

20.945 

79.030 

The  percentage,  as  well  as  the  absolute  quantity  of  car- 
bonic acid,  is  seen  to  stand  in  close  relation  with  the  or- 
ganic matters  of  the  soil.  The  influence  of  the  recent 
application  of  manure  rich  in  organic  substances  is  strik- 
ingly shown  in  case  of  the  asparagus  bed  and  the  sandy 
soil.  The  lowest  percentage  of  carbonic  acid  is  10  times 
that  of  the  atmosphere  a  few  feet  above  the  surface  of  the 
earth,  as  determined  at  the  same  time,  while  the  highest 
percentage  is  390  times  that  proportion. 

Even  in  the  sandy  subsoil  the  quantity  of  free  carbonic 
acid  is  as  great  as  in  an  equal  bulk  of  the  atmosphere ; 
and  in  the  cultivated  soils  it  is  present  in  from  6  to  95 


220  HOW   CKOPS   E'EED. 

times  greater  amount.  In  other  words,  in  the  cultivated 
soils  taken  to  the  depth  of  14  inches,  there  was  found  as 
much  carbonic  acid  gas  as  existed  in  the  same  horizontal 
area  of  the  atmosphere  through  a  height  of  7  to  110  feet. 

The  accumulation  of  such  a  percentage  of  carbonic  acid 
gas  in  the  interstices  of  the  soil  demonstrates  the  rapid 
formation  of  this  substance,  which  must  as  rapidly  difluse 
oif  into  the  air.  The  roots,  and,  what  is  of  more  signifi- 
cance, the  leaves  of  crops,  are  thus  far  more  copiously  fed 
with  this  substance  than  were  they  simply  bathed  by  the 
free  atmosphere  so  long  as  the  latter  is  unagitated. 

When  the  wind  blows,  the  carbonic  acid  of  the  soil  is 
of  less  account  in  feeding  vegetation  compared  with  that 
of  the  atmosphere.  When  the  air  moves  at  the  rate  of 
two  feet  per  second,  the  current  is  just  plainly  perceptible. 
A  mass  of  foliage  2  feet  high  and  200  feet  *  long,  situated 
in  such  a  current,  would  be  swept  by  a  volume  of  atmos- 
phere, amounting  in  one  minute  to  48,000  cubic  feet,  and 
containing  12  cubic  feet  of  carbonic  acid.  In  one  hour  it 
would  amount  to  2,280,000  cubic  feet  of  air,  equal  to  720 
cubic  feet  of  carbonic  acid,  and  in  one  day  to  69,120,000 
cubic  feet  of  air,  containing  no  less  than  17,280  cubic  feet 
of  carbonic  acid. 

In  a  brisk  wind,  ten  times  the  above  quantities  of  air 
and  carbonic  acid  would  pass  by  or  through  the  foliage. 
It  is  plain,  then,  that  the  atmosphere,  which  is  rarely  at 
rest,  can  supply  carbonic  acid  abundantly  to  foliage  with- 
out the  concourse  of  the  soil.  At  the  same  time  it  should 
not  be  forgotten  that  the  carbonic  acid  of  the  atmosj^here 
is  largely  derived  from  the  soil. 

Carbonic  Acid  in  the  Water  of  tSie  Soil,— ^^otwith- 
standing  the  presence  of  so  much  carbonic  acid  in  the  air 
of  the  soil,  it  appears  that  the  capillary  soil-water,  or  so 


*  A  square  field  containing  one  acre  is  208  feet  and  a  few  inches  on  eacli  side. 


THE    AIR    OP    THE    SOIL.  221 

much  of  it  as  may  be  expressed  by  pressure,  is  not  nearly 
saturated  with  this  gas. 

De  Saussure  {Becherches  Ghimiques  sur  la  Vegetatioti, 
p.  168)  filled  large  vessels  with  soils  HcA  m  organic  mat- 
ters^ poured  on  as  much  water  as  the  earth  could  imbibe, 
allowing  the  excess  to  drain  off  and  the  vessels  to  stand 
five  days.  Then  the  soils  were  subjected  to  powerful 
pressure,  and  the  water  thus  extracted  was  examined  for 
carbonic  acid.  It  contained  but  2°|q  of  its  volume  of  the 
gas. 

Since  at  a  medium  temperature  (60°  F.)  water  is  capa- 
ble of  dissolving  100°  [^  (its  own  bulk)  of  carbonic  acid,  it 
would  appear  on  first  thought  inexplicable  that  the  soil- 
water  should  hold  but  2  per  cent.  Henry  and  Dalton  long 
ago  demonstrated  that  the  relative  proportion  in  wliich 
the  ingredients  of  a  gaseous  mixture  are  absorbed  by  wa- 
ter depends  not  only  on  the  relative  solubility  of  each  gas 
by  itself,  but  also  on  the  proportions  in  which  they  exist 
in  the  mixture.  The  large  quantities  of  oxygen,  and 
especially  of  nitrogen,  associated  with  carbonic  acid  in  the 
pores  of  the  soil,  thus  act  to  prevent  the  last-named  gas 
being  taken  up  in  greater  amount ;  for,  while  carbonic 
acid  is  about  fifty  times  more  soluble  than  the  atmos- 
pheric mixture  of  oxygen  and  nitrogen,  the  latter  is  pres- 
ent in  fifty  times  (more  or  less)  the  quantity  of  the  former. 

Absorption  of  Carbonic  Acid  by  the  Soil. — ^According  to 
Yan  den  Broek,  [Ann.  der  Chemie  u,  PA.,  115,  p.  87)  certain 
wells  in  the  vicinity  of  Utrecht,  Holland,  which  are  exca- 
vated only  a  few  feet  deep  in  the  soil  of  gardens,  contain 
water  which  is  destitute  of  carbonic  acid  (gives  no  precipi- 
tate with  lime-water),  while  those  which  penetrate  into  the 
underlying  sand  contain  large  quantities  of  carbonate  of 
lime  in  solution  in  carbonic  acid. 

Yan  den  Broek  made  the  following  experiments  with 
garden-soil  newly  manured,  and  containing  free  carbonic 
acid  in  its  interstices,  which  could  be  displaced  by  a  cur- 


222  HOW    CEOPS    FEED. 

rent  of  air.  *  Tbrougli  a  mass  of  this  earth  20  inches  deep 
and  3  inches  in  diameter,  pure  distilled  water  (free 
from  carbonic  acid)  was  allowed  to  filter.  It  ran  through 
without  taking  up  any  of  the  gas.  Again,  water  contain- 
ing its  own  volume  of  carbonic  acid  was  filtered  through 
a  similar  body  of  the  same  earth.  This  water  gave  up  all 
its  carho7iic  acid  while  in  contact  loith  the  soil.  After  a 
certain  amount  had  run  off,  however,  the  subsequent  j^or- 
tions  contained  it.  In  other  words,  the  soils  experiment- 
ed with  were  able  to  absorb  carbonic  acid  from  its  aqueous 
solution,  even  when  their  interstices  contained  the  gas  in 
the  free  state.  These  extraordinary  phenomena  deserve 
further  study. 

§   3. 

NON-NITROGENOUS  ORGANIC  MATTERS  OF  THE  SOIL.— 

CARBOHYDRATES.     VEGETABLE  ACIDS.     VOLATILE 

ORGANIC  ACIDS.     HUMUS. 

Carbohydrates,  or  Bodies  of  the  Cellulose  Group.— 

The  steps  by  which  organic  matters  become  incorporated 
with  the  soil  have  been  recounted  on  p.  135.  When  plants 
perish,  their  proximate  principles  become  mixed  with  the 
soil.  These  organic  matters  shortly  begin  to  decay  or  to 
pass  into  humus.  In  most  circumstances,  however,  the 
soil  must  contain,  temporarily  or  j)eriodically,  unalter- 
ed carbohydrates.  Cellulose,  especially,  may  be  often 
found  in  an  unaltered  state  in  the  form  of  fragments  of 
straw,  etc. 

De  Saussure  {Recherches,  p.  174)  found  that  water  dis- 
solved from  a  rich  garden  soil  that  had  been  highly  ma- 
nured for  a  long  time,  several  thousandths  of  organic 
matter,  giving  an  extract,  which,  when  concentrated,  had 
an  almost  syrupy  consistence  and  a  sweet  taste,  was 
neither  acid  nor  alkaline  in  reaction,  and  comported  itself 
not  unlike  an  impure  mixture  of  glucose  and  dextrin. 


OKGANIC    MATTERS    OF    THE    SOIL.  223 

Verdeil  and  R-isler  have  made  similar  observations  on  ten 
soils  from  the  farm  of  the  Institut  Agronomique^  at  Yer- 
sailles.  They  found  that  the  water-extract  of  these  soils 
contained,  on  the  average,  50°  1^  of  organic  matter,  which, 
when  strongly  heated,  gave  an  odor  like  burning  paper  or 
sugar.  These  observers  make  no  mention  of  creuates  or 
apocrenates,  and  it,  perhaps,  remains  somewhat  doubtful, 
therefore,  whether  their  researches  really  demonstrate  the 
presence  in  the  soil  of  a  neutral  body  identical  with,  or 
allied  to,  dextrin  or  sugar. 

Cellulose,  starch,  and  dextrin,  pass  by  fermentation  into 
sugar  (glucose) ;  this  may  be  resolved  into  lactic  acid  (tlie 
acid  of  sour  milk  and  sour-krout),  butyric  acid  (one  of  the 
acids  of  rancid  butter),  and  acetic  acid  (the  acid  of  vine- 
gar). It  must  often  happen  that  the  bodies  of  the  cellu- 
lose group  ferment  in  the  soil,  the  same  as  in  the  souring 
of  milk  or  of  dough,  though  they  suffer  for  the  most  part 
conversion  into  humus,  as  will  be  shortly  noticed. 

Tej^etable  Acids,  viz.,  oxalic,  malic,  tartaric,  and  citric 
acids,  become  ingredients  of  the  soil  when  vegetable  mat- 
ters are  buried  in  it.  When  the  leaves  of  beets,  tobacco, 
and  other  large-leaved  plants  fall  upon  the  soil,  oxalic  and 
malic  acids  may  pass  into  it  in  considerable  quantity. 
Falling  fruits  may  give  it  citric,  malic,  and  tartaric  acids. 
These  acids,  however,  speedily  suffer  chemical  change 
when  in  contact  with  decaying  albuminoids.  Buchner  has 
shown  {A.n7i.  Ch.  u.  JPh.,  78,  207)  that  the  solutions  of 
salts  of  the  above-named  vegetable  acids  are  rapidly  con- 
verted into  carbonates  when  mixed  with  vegetable  fer- 
ments. In  this  process  tartaric  and  citric  acids'  are  first 
partially  converted  into  acetic  acid,  and  this  subsequently 
passes  into  carbonic  acid. 

Volatile  OrgaHic  Acids. — Formic,  propionic,  acetic,  and 
butyric  acids,  or  rather  their  salts,  have  been  detected  by 
Jongbloed  and  others  in  garden  earth.     They  are  common 


224  HOW    CKOPS    FEED. 

products  of  fermentation,  a  process  that  goes  on  in  the 
juices  of  plants  that  have  become  a  part  of  the  soil  or  of 
a  compost. 

These  acids  can  scarcely  exist  in  the  soil,  except  tempo- 
rarily, as  results  of  fermentation  or  decay,  and  then  in  but 
very  minute  quantity.  Tbey  consist  of  carbon,  hydrogen, 
and  oxygen.  Their  salts  are  all  freely  soluble  in  water. 
Their  relations  to  agricultural  plants  have  not  been  studied. 

Humus  (in  part). — The  general  nature  and  origin  of 
humus  has  been  already  considered.  It  is  the  debris  of 
vegetation  (or  of  animal  matters)  in  certain  stages  of  de- 
composition. Humus  is  considerably  complex  in  its 
chemical  character,  and  our  knowledge  of  it  is  confessedly 
incomplete.  In  the  paragraphs  that  immediately  follow, 
we  shall  give  from  the  best  sources  an  account  of  its  non- 
nitrogenous  ingredients,  so  far  they  are  understood,  reserv- 
ing to  a  later  chapter  an  account  of  its  nitrogenized  con- 
stituents. 

The  Non-nitrog€HOus   Components  of  Humus,— The 

aj^pearance  and  composition  of  humus  is  different,  accord- 
ing to  the  circumstances  of  its  formation.  It  has  already 
been  mentioned  that  humus  is  brown  or  black  in  color. 
It  appears  that  the  first  stage  of  decomposition  yields  the 
brown  humus.  It  is  seen  in  the  dead  leaves  hanging  to  a 
tree  in  autumn,  in  the  upper  layers  of  fallen  leaves,  in  the 
outer  bark  of  trees,  in  the  smut  of  wheat,  and  in  the  up- 
per, dryer  portions  of  peat. 

When  brown  humus  remains  wet  and  with  imperfect 
access  of  air,  it  decomposes  further,  and  in  time  is  convert- 
ed into  black  humus.  Black  humus  is  invariably  found 
in  the  soil  beyond  a  little  depth  especially  if  it  be  com- 
pact, in  the  deeper  layers  of  peat,  in  the  interior  of  com- 
post heaps,  in  the  lower  portions  of  the  leaf-mould  of 
forests,  and  in  the  mud  or  muck  of  swamps  and  jDonds. 

Ulmic  Acid    and    Vlmm. — The  brown  humus  contains 


OEGANIC   MATTERS    OF   THE    SOIL.  225 

(besides,  perhaps,  unaltered  vegetable  matters)  t^\^o  char- 
acteristic ingredients,  which  have  been  designated  ulmic 
acid  and  idmin,  (so  named  from  having  been  found  in  a 
brown  mass  that  exuded  from  an  elm  tree,  ulmus  being 
the  Latin  for  elm).  These  two  bodies  demand  particular 
notice. 

When  brown  peat  is  boiled  with  water,  it  gives  a  yel- 
lowish or  pale-brown  liquid,  being  but  little  soluble  in 
pure  water.  If,  however,  it  be  boiled  with  dilute  solution 
of  carbonate  of  soda  (sal-soda),  a  dark-brown  liquid  is 
obtained,  which  owes  its  color  to  ulmate  of  soda.  The 
alkali  dissolves  the  insoluble  ulmic  acid  by  combining 
with  it  to  form  a  soluble  compound.  By  repeatedly  heat- 
ing the  same  portion  of  peat  with  new  quantities  of  sal- 
soda  solution,  and  j)ouring  off  the  liquids  each  time,  there 
arrives  a  moment  when  the  peat  no  longer  yields  any  color 
to  the  solution.  The  brown  peat  is  thus  separated  into 
one  portion  soluble,  and  another  insoluble,  in  carbonate  of 
soda.  Tllmic  acid  has  passed  into  the  solution,  and  ulmin^ 
remains  undissolved  (mixed,  it  may  be,  with  unaltered 
vegetable  matters,  recognizable  by  their  form  and  struc- 
ture, and  with  sand  and  mineral  substances). 

By  adding  hydrochloric  acid  to  the  brown  solution  as 
long  as  it  foams  or  effervesces,  the  ulmic  acid  separates  in 
brown,  bulky  flocks,  and  is  insoluble  in  dilute  hydrochloric 
acid,  but  is  a  little  soluble  in  pure  water.  When  moist,  it 
has  an  acid  reaction,  and  dissolves  readily  in  alkalies  or 
alkali-carbonates.  On  drying,  the  ulmic  acid  shrinks 
greatly  and  remains  as  a  brown,  coherent  mass. 

The  ulmin^  which  remains  after  treatment  of. brown 
peat  with  carbonate  of  soda  is  an  indifferent,  neutral  (i.  e., 
not  acid)  body,  which  has  the  same  composition  as  the 


*  The  above  statement  is  made  on  the  authority  of  Mulder.  The  writer  has, 
however,  found,  in  several  cases,  that  continued  treatment  with  carbonate  of 
Boda  alone  completely  dissolves  the  humus,  leaving  a  residue  of  cellulose  Avhich 
yields  nothing  to  caustic  alkali.  He  is,  therefore,  inclined  to  disbelieve  in  the 
existence  of  ulmin  and  humin  as  distinct  from  ulmic  and  humic  acids. 


226  HOW    CROPS    FEED. 

ulmic  acid.  By  boiling  it  with  caustic  soda  or  potash-lye, 
it  is  converted  without  change  of  composition  into  ulmic 
acid. 

On  gently  heating  sugar  with  dilute  hydrochloric  acid, 
a  brown  substance  is  produced,  which  appears  to  be  iden- 
tical with  the  ulmic  acid  obtained  from  peat. 

Humic  Acid  and  Mumill. — By  treating  black  humus 
with  carbonate  of  soda  as  above  described,  it  is  separated 
into  humic  acid  and  hurain^^  which  closely  resemble  ulmic 
acid  and  ulmin  in  all  their  properties — possess,  however,  a 
black  color,  and,  as  it  appears,  a  somewhat  different  com- 
position. 

Humic  acid  and  humin  may  be  obtained  also  by  the 
action  of  hot  and  strong  hydrochloric  acid,  of  sulphuric 
acid,  and  of  alkalies,  upon  sugar  and  the  other  members 
of  the  cellulose  group. 

Composition  ©f  Ulmin,  Ulmic  Acid,  Mnmin,  and  Humic 
Acid, — The  results  of  the  analyses  of  these  bodies,  as  ob- 
tained by  different  experimenters  and  from  different 
sources,  are  not  in  all  cases  accordant.  Either  several  dis- 
tinct substances  have  been  confounded  under  each  of  the 
above  names,  or  the  true  ulmin  and  humin,  and  ulmic  and 
humic  acids,  are  liable  to  occur  mixed  with  other  matters, 
from  which  they  cannot  be  or  have  not  been  perfectly 
separated. 

Mulder  {Chemie  der  Ackerlcrume^  1,  p.  322),  who  has 
chiefly  investigated  these  substances,  believes  there  is  a 
group  of  bodies  having  in  general  the  characters  of  ulmin 
and  ulmic  acid,  whose  composition  differs  only  by  the  ele- 
ments of  water,f  and  is  exhibited  by  the  general  formula 

0„  H,,  O.,  +  nH,0, 
in  which  nH^O  signifies  one,  two,  three,  or  more  of  water 


*  See  note  on  page  225. 

t  In  a  way  analogous  to  what  is  known  of  the  sugars.    (H.  C.  G.,  p.  80.) 


orgaxic  matters  of  the  soil.  227 

Illmic  acid  from  sugar  has  the  following  composition  in 
100  parts : 

Carbon,         67.1 

Hydrogen,      4.2 

Oxygen,       28.7 


100.0 
which  corresponds  to  C^^,  H^g  O^^  H^O. 

Mulder  considers  that  in  the  same  manner  there  exist 
various  kinds  of  humic  acids  and  humin,  differing  from 
each  other  by  the  elements  of  water,  all  of  which  may 
be  represented  by  the  general  formula  C^^  H^^  Oj^  nH^O. 
Humic  acid  and  humin  from  sugar,  corresponding  to 
C^^  H^^  Oj„  +  SH^O,  have,  according  to  Mulder,  the  fol- 
lowing composition  per  cent : 

Carbon,  64 
Hydrogen,  4 
Oxygen,        32 


100 


Apocrenic  and  Creaic  Acids* — In  the  acid  liquid  from 
which  ulmic  or  humic  acid  has  been  separated,  exist  two 
other  acids  which  were  first  discovered  by  Berzelius  in 
the  Porla  spring  in  Sweden,  and  which  bear  the  names 
apocrenic  acid  and  crenic  acid  respectively.  By  adding 
soda  to  the  acid  liquid  until  the  hydrochloric  acid  is  neu- 
tralized, then  acetic  acid  in  slight  excess,  and  lastly  solu- 
tion of  acetate  of  copper  (crystallized  verdigris)  as  long 
as  a  dirty-gray  precipitate  is  formed,  the  apocrenic  acid  is 
procured  in  combination  with  copper  and  ammonia.  From 
this  salt  the  acid  itself  may  be  separated*  as  a  brown, 
gummy  mass,  which  is  easily  soluble  in  water.  Accord- 
ing to  Mulder  it  has  the  formula  C^^  H^^  0^„  +  H^O,  or, 
in  100  parts, 


*  By  precipitating  the  copper  with  sulphuretted  hydrogen. 


228  HOW    CROPS    FEED. 

Carbon,  56.47 
Hydrogen,  2.75 
Oxygen,       40.78 


100.00 
Crenate  of  copper  is  lastly  precipitated  as  a  grass-green 
substance  by  adding  acetate  of  copper  to  the  liquid  from 
wliich  the  apocrenate  of  copper  was  separated,  and  then 
neutralizing  tlie  free  acid  with  ammonia.  From  this  com- 
pound crenic  acid  may  be  prepared  as  a  white,  solid  body 
of  sour  taste,  to  which  Mulder  ascribes  the  formula  C„^ 
^24  ^16  +  ^H^O,  and  in  100  parts  the  following  compo- 
sition • 

Carbon,        45.70 

Hydrogen,    4.80 

Oxygen,      49.50 


100.00 
Mutual  Conversion  of  ipocrenic  and  Crenic  Acids. 

— When,  on  the  one  hand,  apocrenic  acid  is  placed  in 
contact  with  zinc  and  dilute  sulphuric  acid,  the  hydrogen 
evolved  from  the  latter  converts  the  brown  apocrenic  acid 
(by  uniting  with  a  portion  of  its  oxygen)  into  colorless 
crenic  acid.  On  the  other  hand,  the  solution  of  crenic 
acid  exposed  to  the  air  shortly  becomes  brown  by  absorp- 
tion of  oxygen  and  formation  of  apocrenic  acid.  These 
changes  may  be  repeated  many  times  with  the  same  por- 
tion of  these  substances. 

Mulder  remarks  ( Chemie  der  Ackerkrume^  p.  350) : 
"  In  every  fertile  soil  these  acids  always  occur  together  in 
not  inconsiderable  quantities.  When  the  earth  is  turned 
over  by  the  plow,  two  essentially  different  processes  fol- 
low each  other :  oxidation,  where  the  air  has  free  access  ; 
reduction,  Avhere  its  access  is  more  or  less  limited  by  the 
adhesion  of  the  particles  and  especially  by  moisture.  In 
the  loose,  dry  earth  apocrenic  acid  is  formed ;  in  the  firm, 


ORGANIC   MATTERS    OF   THE    SOIL.  229 

moist  soil,  and  in  every  soil  after  rain,  crenic  acid  is  pro- 
duced, so  that  the  action  or  effects  of  these  substances  are 
alternately  manifested." 

The  Humus   Bodies   Artificially  Produced. —  When 

sugar,  cellulose,  starch,  or  gum,  is  boiled  with  strong  hy- 
drochloric acid  or  a  strong  solution  of  potash,  brown  or 
black  bodies  result  which  have  the  greatest  similarity  with 
the  ulmin  and  humin,  the  ulmic  and  humic  acids  of  peat 
and  of  soils. 

By  heating  humus  with  nitric  acid  (a  vigorous  oxidizing 
agent),  crenic  and  apocrenic  acids  are  formed.  The  pro- 
duction of  these  bodies  by  such  artificial  means  gives  in- 
teresting confirmation  of  the  reality  of  their  existence, 
and  demonstrates  the  correctness  of  the  views  which  have 
been  advanced  as  to  their  origin. 

While  the  precise  composition  of  all  these  substances 
may  well  be  a  matter  of  doubt,  and  from  the  difficulties 
of  obtaining  them  in  the  pure  state  is  likely  to  remain  so, 
their  existence  in  the  soil  and  their  importance  in  agricul- 
tural science  are  beyond  question,  as  we  shall  shortly  have 
opportunity  to  understand. 

Tlie   Condition  of  these   Humus   Bodies  In  the   Soil 

requires  some  comment.  The  organic  substances  thus 
noticed  as  existing  in  the  soil  are  for  the  most  part  acids, 
but  they  do  not  exist  to  much  extent  in  the  free  state,  ex- 
cept in  bogs  and  morasses.  A  soil  that  is  fit  for  agricul- 
tural purposes  contains  little  or  no  free  acid,  except  car- 
bonic acid,  and  oftentimes  gives  an  alkaline  reaction  with 
test-papers. 

Regarding  ulraic  and  humic  acids,  which,  as  we  have 
stated,  are  extracted  by  solution  of  carbonate  of  soda 
from  humus,  it  appears  that  they  do  not  exhibit  acid  char- 
acters before  treatment  with  the  alkali.  They  appear  to 
be  altered  by  the  alkali  and  converted  through  its  influ- 
ence  into  acids.     Only  those  portions  of   these   bodies 


230  now  CK0P3  fjeed. 

which  are  acted  upon  by  the  carbonates  of  potash,  soda, 
and  lime,  that  become  ingredients  of  the  soil  by  the 
solution  of  rocks,  or  by  carbonate  of  ammonia  brought 
down  from  the  atmosphere  or  produced  by  decay  of  ni- 
trogenous matters,  acquire  solubility,  and  are,  in  fact, 
acids;  and  these  portions  are  acids  in  combination  (salts), 
and  not  in  the  free  state. 

Tfee  Salts  ef  the  Humus  Acids  that  may  exist  in  the 
soil,  viz.,  the  ulmates,  humates,  apocrenates,  and  crenates 
of  potash,  soda,  ammonia,  lime,  magnesia,  iron,  manga- 
nese, and  alumina,  require  notice. 

The  uhnates  and  humates  agree  closely  in  their  charac- 
ters so  far  as  is  kuown. 

The  ulmates  and  humates  of  the  alkalies  (potash,  soda, 
and  ammonia)  Vive  freely  soluble  in  water.  They  are  formed 
when  the  alkalies  or  their  carbonates  come  in  contact  1st, 
with  the  ulmic  and  humic  acids  themselves  ;  2d,  with  the 
ulmates  and  humates  of  lime,  magnesia,  iron,  and  manga- 
nese ;  and  3d,  by  the  action  of  the  alkalies  and  their  car- 
bonates on  humin  and  ulmin.  Their  solutions  are  yellovv^ 
or  brown. 

The  ulmates  and  humates  of  lime,  magnesia,  iron,  man- 
ganese, and  alumina,  are  insoluble^  or  but  very  slightly 
soluble  171  water. 

From  ordinary  soils  where  these  earths  and  oxides  pre- 
dominate, water  removes  but  traces  of  humates  and 
ulmates. 

From  peat,  garden  earth,  and  leaf-mould,  which  contain 
excess  of  the  humic  and  ulmic  acids,  and  carbonate  of 
ammonia  resulting  from  the  decay  of  nitrogenous  matters, 
water  extracts  a  perceptible  amount  of  these  acids  render- 
ed soluble  by  the  alkali. 

There  appear  to  exist  double  salts  of  humic  acid  and  of 
ulmic  acid,  i.  e.,  salts  containing  the  acid  combined  with  two 
or  more  bases.  By  adding  solutions  of  compounds  (e.  g., 
sulphates)  of  Ihne,  magnesia,  iron,  manganese,  and  alumina 


ORGANIC   MATTERS    OF    THE    SOIL.  231 

to  solutions  of  humates  or  nlmates  of  the  alkalies,  precipi- 
tates are  formed  in  which  the  acid  is  combined  both  with 
an  alkali  and  an  earth  or  oxide.  These  double  salts  are 
insoluble  or  nearly  so  in  water. 

Solutions  of  alkalies  and  alkali  carbonates  decompose 
them  into  soluble  alkali  humates  or  ulmates,  and  the 
earths  or  oxides  are  at  least  partially  held  in  solution  by 
the  resulting  compounds. 

Mulder  describes  the  following  experiraents,  wbich  justify  the  above 
conclusions.  "Garden-soil  was  extracted  with  dilute  solution  of  car- 
bonate of  soda,  the  soil  being  in  excess.  The  solution  was  filtered  and 
precipitated  by  addition  of  water,  and  the  precipitate  was  washed  and  dis- 
solved in  a  little  ammonia.  Thus  was  obtained  a  dark -brown  solution 
of  neutral  humate  of  ammonia.  The  solution  was  rendered  perfectly 
colorless  by  addition  of  caustic  lime — basic  humate  of  lime  is  therefore 
perfectly  insoluble  in  water. 

"Chloride  of  calcium  rendered  the  solution  very  nearly  colorless — 
neutral  humate  of  lime  is  almost  entirely  insoluble. 

"Calcined  magnesia  decolorized  the  solution  perfectly.  Chloride  of 
magnesium  made  the  solution  very  nearly  colorless. 

"The  sulphates  of  protoxide  and  iDcroxide  of  iron,  and  sulphate  of 
manganese,  decolorized  the  solution  perfectly. 

"  These  decolorized  liquids  were  made  brown  again  by  agitating  them 
and  the  precipitated  humates  with  carbonate  of  ammonia." 

Apocrenates  and  Crenates. — According  to  Mulder,  the 

crenates  and  apocrenates  of  the  soil  nearly  always  contain 
ammonia — are,  in  fact,  double  salts  of  this  alkali  with  lime, 
iron,  etc. 

The  apocrenates  of  the  alkalies  are  freely  soluble ; 
those  of  the  oxides  of  iron  and  manganese  are  moderately 
soluble;  those  of  lime,  magnesia,  and  alumina,  are  in- 
soluble. 

The  crenates  of  the  alkalies,  of  lime,  magnesia,  and 
protoxide  of  iron,  are  soluble ;  those  of  jDrotoxide  of  iron 
and  manganese  are  less  soluble;  crenate  of  alumina  is 
insoluble. 

All  the  salts  of  these  acids  that  are  insoluble  of  them- 
selves are  decomposed  by,  and  soluble  in,  excess  of  the 
alkali-salts. 


232  HOW    CROPS    FEED. 

Do  the  Organic  Matters  of  the  Soil  Directly  Nourish 

Vegetation  ] — This  is  a  question  which,  so  far  as  humus  is 
concerned,  has  been  discussed  with  great  earnestness  by 
the  most  prominent  writers  on  Agricultural  Science. 

De  Saussure,  Berzelius,  and  Mulder,  have  argued  in  the 
affirmative ;  while  Liebig  and  his  numerous  adherents  to- 
tally deny  to  humus  the  possession  of  any  nutritive  value. 
It  is  probable  that  humus  may  be  directly  absorbed  by, 
and  feed,  plants.  It  is  certain,  also,  that  it  does  not  con- 
tribute largely  to  the  sustenance  of  agricultural  crops. 

To  ascertain  the  real  extent  to  which  humus  is  taken  up 
by  plants,  or  even  to  demonstrate  that  it  is  taken  up  by 
them,  is,  perhaps,  impossible  from  the  data  novv^  in  our 
possession.     We  shall  consider  the  probabilities. 

There  have  not  been  wanting  attempts  to  ascertain  ex- 
perimentally whether  humus  is  capable  of  feeding  vegeta- 
tion. Hartig,  De  Saussure,  Wiegmann  and  Polstorf,  and 
Soubeiran,  have  observed  the  growth  of  plants  whose 
roots  were  immersed  in  solutions  of  humus.  The  experi- 
ments of  Hartig  led  this  observer  to  conclude  that  humate 
of  potash  and  water-extract  of  peat  do  not  enter  the  roots 
of  plants.  'Not  having  had  access  to  the  original  account 
of  this  investigation,  the  writer  cannot,  perhaps,  judge 
properly  of  its  merits.  It  appears,  however,  that  the 
roots  of  the  plants  operated  with  were  not  kept  constantly 
moist,  and  their  extremities  were  decomposed  by  too  great 
concentration  of  the  liquid  in  which  they  were  immersed. 
Under  such  conditions  accurate  results  were  out  of  the 
cjuestion. 

De  Saussure  {An7i.  Ch.  u.  JPh.^  42,  275)  made  two  ex- 
periments, one  with  a  bean,  the  other  with  Polygonum 
Persicaria^  in  which  these  plants  were  made  to  vegetate 
with  their  roots  immersed  in  a  solution  of  humate  of  pot- 
ash (prepared  by  boiUng  humus  with  bicarbonate  of  pot- 
ash). In  the  first  case  the  bean  plant,  originally  weigliing 
11   grams,  gained    during   14  days   6    grms.,  while    the 


ORGAXIC    MATTERS    OF    THE    SOIL.  233 

weight  of  the  humus  decreased  9  milligrams.  The 
Polygonum  during  10  days  gained  3,5  grms.,  and  the 
solution  lost  43  milligrams  of  humus.  These  experi- 
ments Liebig  considers  undecisive,  because  an  alkali- 
humate  loses  weight  by  oxidation  (to  carbonic  acid  and 
water)  when  exposed  in  solution  to  the  air.  Mulder,  how- 
ever, denies  that  any  appreciable  loss  could  occur  in  such 
a  solution  during  the  time  of  experiment,  and  considers 
the  trials  conclusive. 

In  a  third  experiment,  De  Saussure  placed  the  roots  of 
Polygonum  Persicaria  in  the  water-extract  of  turf  con- 
taining no  humic  acid  but  crenic  and  apocrenic  acids, 
where  they  remained  nine  days  in  a  very  flourishing  state, 
putting  forth  new  roots  of  a  healthy  white  color.  An 
equal  quantity  of  the  same  extract  was  placed  in  a  simi- 
lar vessel  for  purposes  of  comparison.  It  was  found  that 
the  solution  in  which  the  plants  were  stationed  became 
paler  in  color  and  remained  perfectly  clear,  while  the  other 
solution  retained  its  original  dark  tint  and  became  turbid. 
The  former  left  after  evaporation  33  mgrms.,the  latter  39 
mgrms.  of  solid  residue.  The  difference  of  6  mgrms.,  De 
Saussure  believes  to  have  been  absorbed  by  the  plant. 

Wiegmann  and  Polstorf  (  Ueber  die  unorganischen  Be- 
standtheile  der  Pflanzen)  experimented  in  a  similar  man- 
ner with  Mentha  undidata^  a  kind  of  mint,  and  Polygonum 
Persicaria^  using  two  plants  of  8  inches  height,  whose 
roots  were  well  developed  and  perfectly  healthy.  The 
plants  grew  for  30  days  in  a  wine-yellow  water-extract 
of  leaf  compost  (containing  148  mgrms.  of  solid  sub- 
stance— organic  matter,  carbonate  of  lime,  etc., — in  100 
grams  of  extract),  the  roots  being  shielded  from  light, 
and  during  the  same  time  an  equal  quantity  of  the  same 
solution  stood  near  by  in  a  vessel  of  the  same  dimensions. 
The  plants  grew  well,  increasing  6|-  inches  in  length,  and 
put  forth  long  roots  of  a  healthy  white  color.  On  the 
18th  of  July  the  plants  were  removed  from  the  solution, 


234  HOW    CROPS    FEED. 

and  100  grams  of  the  solution  left  on  evaporation  132 
mgrms.  of  residue.  The  same  amount  of  humus  extract, 
that  had  been  kept  in  a  contiguous  vessel  containing  no 
plant,  left  a  residue  of  136  mgrms.  The  disappearance  of 
humus  from  the  solution  is  thus  mostly  accounted  for  by 
its  oxidation. 

De  Saussure  considers  that  his  experiments  demonstrate 
that  humic  acid  and  (in  his  third  exp.)  the  matters  ex- 
tracted from  peat  by  water  (crenic  and  apocrenic  acids) 
are  absorbed  by  plants.  Wiegmann  and  Polstorf  attrib- 
ute any  apparent  absorption  in  their  trials  to  the  una- 
voidable errors  of  experiment.  The  quantities  that  may 
have  been  absorbed  were  indeed  small,  but  in  our  judg- 
ment not  smaller  than  ought  to  be  estimated  with  certainty. 

Other  experiments  by  Soubeiran,  Malaguti,  and  Mulder, 
are  on  record,  mostly  agreeing  in  this,  viz.,  that  agricul- 
tural plants  (beans,  oats,  cresses,  peas,  barley)  grow  well 
when  their  roots  are  immersed  in,  or  watered  by,  solutions 
of  humates,  ulmates,  crenates,  and  apocrenates  of  ammo- 
nia and  potash.  These  experiments  are,  however,  all  un- 
adapted  to  demonstrate  that  humus  is  absorbed  by  plants, 
and  the  trials  of  De  Saussure  and  of  Wiegmann,  and  Pol- 
storf,  are  the  only  ones  that  have  been  made  under  condi- 
tions at  all  satisfactory  to  a  just  criticism.  These  do  not, 
perhaps,  conclusively  demonstrate  the  nutritive  function 
of  humus.  It  is  to  be  observed,  however,  that  what  evi- 
dence they  do  furnish  is  in  its  favor.  They  prove  effec- 
tually that  humus  is  not  injurious  to  plants,  though  Liebig 
and  Wolff  have  strenuously  insisted  that  it  is  poisonous. 

Let  us  now  turn  to  the  probabilities  bearing  on  the 
question. 

In  the  first  place  there  are  plants — those  living  in  bogs 
and  flourishing  in  dung-heap  liquor — which  throughout 
the  whole  period  of  their  growth  must  tolerate^  if  not  ab- 
sorb, somewhat  strong  solutions  of  humus. 

Again,  the  cultivated^  soil  invariably  yields  some  humus 


ORGANIC    MATTERS    OF   THE    SOIL.  235 

(we  use  this  word  as  ^  general  collective  term)  to  rain- 
water, and  the  richer  the  soil,  as  made  so  by  manures  and 
judged  of  by  its  productiveness,  the  larger  the  quantity, 
up  to  certain  limits,  of  humus  it  contains.  If,  as  we  have 
seen,  plants  always  contain  silica,  though  this  element  be 
not  essential  to  their  development  (H.  C.  G.,  p.  186),  is  it 
]3robable  that  they  are  able  to  reject  humus  so  constantly 
presented  to  them  under  such  a  variety  of  forms  ? 

Liebig  opposes  the  view  that  humus  contributes  directly 
to  the  nourishment  of  plants  because  it  and  its  compounds 
are  insoluble ;  in  the  same  book,  however,  {Die  Ghemie 
in  ihrer  Anwendung  auf  Agricultur  und  Physiologie^ 
7th  Ed.,  1862)  he  teaches  the  doctrine  that  all  the  food 
of  the  agricultural  plant  exists  in  the  soil  in  an  insoluble 
form.  This  old  objection,  still  maintained,  tallies  poorly 
with  his  new  doctrine.  The  old  objection,  furthermore,  is 
baseless,  for  the  humates  are  as  soluble  as  phosphates, 
which  are  gathered  by  every  plant  and  from  all  soils. 

It  has  been  the  habit  of  Liebig  and  his  adherents  to 
teach  that  the  plant  is  nourished  exclusively  by  the  last 
products  of  the  destruction  of  organic  matter,  viz.,  by  car- 
bonic acid,  ammonia,  nitric  acid,  and  water,  together  with 
the  ingredients  of  ashes.  While  no  one  denies  or  doubts 
that  these  substances  chiefly  nourish  agricultural  plants, 
no  one  can  deny  that  other  bodies  may  and  do  take  part 
in  the  process.  It  is  well  established  that  various  organic 
substances  of  animal  origin,  viz.,  urea,  uric  acid,  and  gly- 
cocoll,  are  absorbed  by,  and  nourish,  agricultural  plants ; 
while  it  is  universally  known  that  the  principal  food  of 
multitudes  of  the  lower  orders  of  plants,  the  fungi,  includ- 
ing yeast,  mould,  rust,  brand,  mushrooms,  are  fed  entirely, 
so  far  as  regards  their  carbon,  on  organic  matters.  Thus, 
yeast  lives  upon  sugar,  the  vinegar  plant  on  acetic  acid, 
the  Peronospora  infestans  on  the  juices  of  the  potato, 
etc.  There  are  many  parasitic  plants  of  a  higher  order 
common  in  our  forests  whose  roots  are  fastened  upon  and 


^ob  HOW    CROPS    FEED. 

absorb  the  juices  of  the  roots  of  trees  ;  such  are  the  beech 
drops  {EpipTiegus)^  pine  drops  {Pterospora)^  Indian  pipe 
(Monotropa) ;  the  last-named  also  grows  upon  decayed 
vegetable  matter. 

The  dodder  ( Ciiscuta)  is  parasitic  upon  living  plants, 
especially  upon  flax,  whose  juices  it  appropriates  often  to 
the  destruction  of  the  crop. 

It  is  indeed  true  that  there  is  a  wide  distinction  between 
most  of  these  parasites  and  agricultural  plants.  The 
former  are  mostly  destitute  of  chlorophyll,  and  appear  to 
be  totally  incapable  of  assimilating  carbon  from  carbonic 
acid.*  The  latter  acquire  certainly  the  most  of  their  food 
from  carbonic  acid,  but  in  their  root-organs  they  contain 
no  chlorophyll ;  there  they  cannot  assimilate  carbon  from 
carbonic  acid.  They  do  assimilate  nitrogen  from  the  or- 
ganic principles  of  urine  ;  what  is  to  hinder  their  obtain- 
ing carbon  from  the  soluble  portions  of  humus,  from  the 
organic  acids,  or  even  from  unaltered  carbohydrates  ? 

De  Saussure,  in  his  investigation  just  quoted  from,  says 
further :  "  After  having  thus  demonstrated  f  the  absorp- 
tion of  humus  by  the  roots,  it  remains  to  speak  of  its  as- 
similation by  the  plant.  One  of  the  indications  of  this 
assimilation  is  derived  from  the  absence  of  the  peculiar 
color  of  humus  in  the  interior  of  the  plant,  which  has  ab- 
sorbed a  strongly  colored  solution  of  humate  of  potash,  as 
compared  to  the  different  deportment  of  coloring  matters 


*  Dr.  Lnck  {Ann.  Chem.  u.  Pharm..,  78,  85)  lias  indeed  shown  that  the  mistle- 
toe {Viscum  album)  decomposes  carbonic  acid  in  the  sunlight,  but  this  plant  has 
greenish-yellow  leaves  containing  cMoropliyll. 

t  We  take  occasion  here  to  say  explicitly  that  the  only  valid  criticism  of  De 
Saussure's  experiment  on  the  Polygonum  supplied  with  humate  of  potash,  is 
Llebig''s,  to  the  effect  that  the  solution  lost  humic  acid  to  the  amount  of  43  milli- 
grams not  as  a  result  of  absorption  by  the  plant,  but  by  direct  oxidation. 
Mulder  and  Soubeiran  both  agree  that  such  a  solution  could  not  lose  perceptibly 
in  this  way.  That  De  Saussure  was  satisfied  that  such  a  loss  could  not  occur, 
would  appear  from  the  fact  that  he  did  not  attempt  to  estimate  it,  as  he  did  in 
the  subsequent  experiment  with  water-extract  of  peat.  If,  now,  Liebig  be  wrong 
in  his  objection  (and  he  has  furnished  no  proof  that  his  statement  is  true),  then 
De  Saussure  has  demo7istrated  that  humic  acid  is  absorbed  by  plants. 


ORGANIC   MATTERS    OF   THE    SOIL.  237 

(such  as  ink)  which  cannot  nourish  the  plant.  The  latter 
(ink,  etc.)  leave  evidences  of  their  entrance  into  the  plant, 
while  the  former  are  changed  and  partly  assimilated. 

"  A  bean  15  inches  high,  whose  roots  were  placed  in  a 
decoction  of  Brazil-wood  (to  which  a  little  alum  had  been 
added  and  which  was  filtered),  was  able  to  absorb  no  more 
than  the  fifth  part  of  its  weight  of  this  solution  without 
wilting  and  dying.  In  this  process  four-fifths  of  its  stem 
was  colored  red. 

''^Polygonum  Persicaria  (on  occasion  an  aquatic  or  bog 
plant)  grew  very  well  in  the  same  solution  and  absorbed 
its  coloring  matter,  but  the  color  never  reached  the  stem. 
The  red  principle  of  Brazil-wood  being  j^artially  assimilat- 
ed by  the  Polygonum^  underwent  a  chemical  change; 
while  in  the  bean,  which  it  was  unable  to  nourish,  it  suf- 
fered no  change.  The  Polygonufm  itself  became  colored, 
and  withered  when  its  roots  were  immersed  in  diluted 
ink." 

Biot  (Comptes  Pendus,  1837,  1,  12)  observed  that  the 
red  juice  of  Phytolacca  decandra  (poke- weed),  when 
poured  upon  the  soil  in  v»'hich  a  white  hyacinth  was  blos- 
soming, was  absorbed  by  the  plant,  and  in  one  to  two 
hours  dyed  the  flowers  of  its  own  color.  After  two  or 
three  days,  however,  the  red  color  disappeared,  the  flow- 
ers becoming  white  again. 

From  the  facts  just  detailed,  we  conclude  that  some 
kinds  of  organic  matters  may  be  absorbed  and  chemically 
changed  (certain  of  them  assimilated)  by  agricultural 
plants. 

We  must  therefore  hold  it  to  be  extremely  probable 
that  various  forms  of  humus,  viz.,  soluble  humates,  ulmates, 
crenates,  and  apocrenates,  together  with  the  other  soluble 
organic  matters  of  the  soil,  are  taken  up  by  plants,  and 
decomposed  or  transformed,  nay,  we  may  say,  assimilated 
by  them. 


238  HOW    CEOPS    FEED. 

A  few  experiments  might  easily  be  devised  which  would 
completely  settle  this  point  beyond  all  controversy. 

Or^aaic  Matters  as  Indirect  Sources  of  Carboa  to 

Plants. — The  decay  of  organic  matters  in  the  soil  supplies 
to  vegetation  considerably  more  carbonic  acid  in  a  given 
tiine  than  would  be  otherwise  at  the  command  of  crops. 
The  quantities  of  carbonic  acid  found  in  various  soils  have 
already  been  given  (p.  219).  The  beneficial  eifects  of  such 
a  source  of  carbonic  acid  in  the  soil  are  sufficiently  obvious 
(p.  128). 

Organic  Matters  not  .Essential  to  the  Growth  of 
Crops. — Although,  on  the  farm,  crops  are  rarely  raised 
without  the  concurrence  of  humus  or  at  least  without  its 
presence  in  the  soil,  it  is  by  no  means  indispensable  to 
their  life  or  full  development.  Carbonic  acid  gas  is  of  it- 
self able  to  supply  the  rankest  vegetation  with  carbon,  as 
has  been  demonstrated  by  numerous  experiments,  in  which 
all  other  compounds  of  this  element  have  been  excluded 
(p.  48). 

§4. 
THE    AMMONIA    OF    THE    SOIL. 

In  the  chapter  on  the  Atmosphere  as  the  food  of  j)lants 
we  have  been  led  to  conclude  that  the  element  nitrogen^ 
so  indispensable  to  vegetation  as  an  ingredient  of  albumin, 
etc.,  is  supplied  to  plants  exclusively  hy  its  compounds^ 
and  mainly  hy  ammonia  and  7iitric  acid,  or  by  substances 
which  yield  these  bodies  readily  on  oxidation  or  decay. 

We  have  seen  further  that  both  ammonia  and  nitric  acid 
exist  in  very  minute  quantities  in  the  atmosphere,  are  dis- 
solved in  tl^e  atmospheric  waters,  and  by  them  brought 
into  the  soil. 

It  is  pretty  fairly  demonstrated,  too,  that  these  bodies, 
as  occurring  in  the  atmosphere,  become  of  appreciable  use 


THE    AMMOXIA    OF    THE    SOIL.  239 

to  agricultural  vegetation  only  after  their  incorporation 
with  the  soil. 

Rain  and  dew  are  means  of  collecting  them  from  the 
atmosphere,  and,  as  ^ve  shall  shortly  see,  the  soil  is  a 
storehouse  for  them  and  the  medium  of  their  entrance  into 
vegetation. 

This  is  therefore  the  proper  place  to  consider  in  detail 
the  origin  and  formation  of  ammonia  and  nitric  acid,  so 
far  as  these  points  have  not  been  noticed  when  discussing 
their  relations  to  the  atmosphere. 

Ammonia  is  formed  ia  tlie  Sol!  either  in  the  decay  of 
organic  bodies  containing  nitrogen,  as  the  albuminoids, 
etc.,  or  by  the  reduction  of  nitrates  (p.  74).  The  former 
process  is  of  universal  occurrence  since  both  vegetable 
and  animal  remains  are  constantly  present  in  the  soil ;  the 
latter  transformation  goes  on  only  under  certain  condi- 
tions, which  will  be  considered  in  the  next  section  (p. 
269). 

The  statement  that  ammonia  is  generated  from  the  free 
nitrogen  of  the  air  and  the  nascent  hydrogen  of  decom- 
posing carbohydrates,  as  cellulose,  starch,  etc.,  or  that  set 
free  from  water  in  the  oxidation  of  certain  metals,  as  iron 
and  zinc,  has  been  completely  disproved  by  Will.  {A?i7i. 
d.   Ch.  XI.  Ph.,  45,  pp.  lOG-112.)  ' 

The  ammonia  encountered  in  such  experiments  may  have  been,  1st, 
tliat  pre-existlni^  in  the  pores  of  the  substances,  or  dissolved  in  the  v/a- 
ter  operated  with.  Faraday  {Researches  in  ChemistrTj  and  Physics^  j).  143) 
has  shown  by  a  series  of  exact  experiments  that  numerous,  we  may  say 
all,  porous  bodies  exposed  to  the  air  have  a  minute  amount  of  ammonia 
adhering  to  them ;  2d,  that  which  is  generated  in  the  process  of  testing 
or  experimenting  (as  when  iron  is  heated  with  potash),  and  fofmed  by 
the  action  of  au  alkali  on  some  compound  of  nitrogen  occurring  in  the 
materials  of  the  experiment ;  or,  8d,  that  which  results  from  the  reduc- 
tion of  a  nitrite  formed  from  free  nitrogen  by  the  action  of  ozone  (pi^. 
77-83). 

The  Ammonia  of  the  Soil. — a.  Gaseous  Ammoiiia  os 
Carhonate. — Boussingault  and  Lewy,  in  their  examination 
of  the  air  contained  in  the  interstices  of  the  soil,  p.  219, 


240  HOW    CBOPS    FEED. 

tested  it  for  ammonia.  In  but  two  instances  did  they  find 
sufficient  to  weigh.  In  all  cases,  however,  they  were  able 
to  detect  it,  though  it  was  present  in  very  minute  quanti- 
ty. The  two  experiments  in  which  they  were  able  to 
weigh  the  ammonia  were  made  in  a  light,  sandy  soil  from 
which  potatoes  had  been  lately  harvested.  On  the  2d  of 
September  the  field  was  manured  with  stable  dung ;  on 
the  4th  the  first  experiment  was  made,  the  air  being  taken, 
it  must  be  inferred  from  the  account  given,  at  a  depth  of 
14  inches.  In  a  million  parts  of  air  by  weight  were  found 
32  parts  of  ammonia.  Five  days  subsequently,  after  rainy 
weather,  the  air  collected  at  the  same  place  contained  but 
13  23arts  in  a  million. 

h.  Ammonia  physically  condensed  in  the  Soil. — Many 
porous  bodies  condense  a  large  quantity  of  ammonia  gas. 
Charcoal,  which  has  an  extreme  porosity,  serves  to  illus- 
trate this  fact.  De  Saussure  found  that  box-wood  char- 
coal, freshly  ignited,  absorbed  98  times  its  volume  of 
ammonia  gas.  Similar  results  have  been  obtained  by  Sten- 
house,  Angus  Smith,  and  others  (p.  166).  The  soil  cannot, 
however,  ordinarily  contain  more  than  a  minute  quantity 
of  physically  absorbed  ammonia.  The  reasons  are,  first,  a 
porous  body  saturated  with  ammonia  loses  the  greater  share 
of  this  substance  when  other  gases  come  in  contact  with 
it.  It  is  only  possible  to  condense  in  charcoal  98  times  its 
volume  of  ammonia,  by  cooling  the  hot  charcoal  in  mer- 
cury which  does  not  penetrate  it,  or  in  a  vacuum,  and  then 
bringing  it  directly  into  the  pui^e  ammonia  gas.  The 
charcoal  thus  saturated  with  ammonia  loses  the  latter  rap- 
idly on  exposure  to  the  air,  and  Stenhouse  has  found  by 
actual  trial  that  charcoal  exposed  to  ammonia  and  after- 
wards to  air  retains  but  minute  traces  of  the  former. 
Secondly,  the  soil  when  adapted  for  vegetable  growth  is 
moist  or  wet.  The  water  of  the  soil  which  covers  the 
particles  of  earth,  rather  than  the  particles  themselves, 
must  contain  any  absorbed  ammonia.     Thirdly,  there  are 


THE    AMMOJS^IA    OF    THE    SOIL.  241 

in  fertile  soils  substances  which  combine  chemically  with 
ammonia. 

That  the  soil  does  contain  a  certain  quantity  of  ammo- 
nia adhering  to  the  surface  of  its  particles,  or,  more  prob- 
ably, dissolved  in  the  hygroscopic  water,  is  demonstrated 
by  the  experiments  of  Boussingault  and  Lev/ y  just  alluded 
to,  in  all  of  which  ammonia  was  detected  in  the  air  in- 
cluded in  the  cavities  of  the  soil.  In  case  ammonia  were 
physically  condensed  or  absorbed,  a  portion  of  it  would 
be  carried  off  in  a  current  of  air  in  the  conditions  of 
Boussingault  and  Lewy's  experiments, — nay,  all  of  it 
would  be  removed  by  such  treatment  sufficiently  prolonged. 

Brustlein  (Boussingault's  Agronomie,  etc.,  1,  -p.  152) 
records  that  100  parts  of  moist  earth  placed  in  a  vessel  of 
about  2^  quarts  capacity  containing  0.9  parts  of  (free) 
ammonia,  absorbed  during  3  hours  a  little  more  than  0.4 
parts  of  the  latter.  In  another  trial  100  parts  of  the  same 
earth  dried,  placed  under  the  same  circumstances,  absorb- 
ed 0.28  parts  of  ammonia  and  2.6  parts  of  water. 

Brustlein  found  that  soil  placed  in  a  confined  atmos- 
phere containing  very  limited  quantities  of  ammonia  can- 
not condense  the  latter  completely.  In  an  experiment 
similar  to  those  just  described,  100  parts  of  earth  (tena- 
cious calcareous  clay)  and  0.019  parts  of  ammonia  were 
left  together  5  days.  At  the  conclusion  of  this  period 
O.OIG  parts  of  the  latter  had  been  taken  up  by  the  earth. 
The  remainder  was  found  to  be  dissolved  in  the  water 
that  had  evaporated  from  the  soil,  and  that  formed  a  dew 
on  the  interior  of  the  glass  vessel. 

Brustlein  proved  further  that  while  air  may  be  almost 
entirely  deprived  of  its  ammonia  by  traversing  a  long 
column  of  soil,  so  the  soil  that  has  absorbed  ammonia 
readily  gives  up  a  large  share  of  it  to  a  stream  of  pure  air. 
He  caused  air,  charged  with  ammonia  gas  by  being  made 
to  bubble  througli  water  of  ammonia,  to  traverse  a  tube  1 
ft.  long  filled  with  small  fragments  of  moist  soil.  The 
11 


242  HOW    CROPS    FEED. 

ammonia  was  completely  absorbed  in  the  first  part  of  the 
experiment.  After  about  7  cubic  feet  of  air  had  streamed 
through  the  soil,  ammonia  began  to  escape  unabsorbed. 
The  earth  thus  saturated  contained  0.192°  1^  of  ammonia. 
A  current  of  pure  air  was  now  passed  through  the  soil  as 
long  as  ammonia  was  removed  by  it  in  notable  quantity, 
about  38  cubic  feet  being  required.  By  this  means  more 
than  one-half  the  ammonia  was  displaced  and  carried  off. 
the  earth  retaining  but  0.084"  |^. 

Brustlein  ascertained  further  that  ammonia  which  has 
been  absorbed  by  a  soil  from  aqueous  solution  escapes 
easily  when  the  earth  is  exposed  to  the  air,  especially 
when  it  is  repeatedly  moistened  and  allowed  to  dry. 

100  parts  of  the  same  kind  of  soil  as  was  employed  in 
the  experiments  already  described  were  agitated  with  187 
parts  of  water  containing  0.889  parts  of  ammonia.  The 
earth  absorbed  0.157  parts  of  ammonia.  It  was  now 
drained  from  the  liquid  and  allowed  to  dry  at  a  low  tem- 
perature, which  operation  required  eight  days.  It  was 
then  moistened  and  allowed  to  dry  again,  and  this  was  re- 
peated four  times.  The  progressive  loss  of  ammonia  is 
shown  by  the  following  figures. 

100  parts  of  soil  absorbed 0.157  parts  of  ammonia. 

"      "       "    "    contained  after  the  first     drying 0.083    "     "  "" 

"      "       "    "  ''  "■      "    second    "      0.066    "      " 

"      "       "    "  "  "      "    third        "      0.054    "      " 

"      "       "     "  "  "      "    fourth      "      0.041    "      " 

"      "       "     "  "  ''      "    fifth         "       0.039    '•      '' 

In  this  instance  the  loss  of  ammonia  amounted  to  three- 
fourths  the  quantity  at  first  absorbed. 

The  extent  to  which  absorbed  ammonia  escapes  from 
the  soil  is  greatly  increased  by  the  evaporation  of  water. 
Brastlein  found  that  a  soil  containing  0.067°  1^  of  ammo- 
nia suffered  only  a  trifling  loss  by  keeping  43  days  in  a 
dry  place,  whereas  the  same  earth  lost  half  its  ammonia 
in  a  shorter  time  by  being  thrice  moistened  and  dried. 

According  to  Knop   {Vs.  jSL,  III,  p.  222),  the  single 


THE    AMMONIA    OF    THE    SOIL.  213 

proximate  ingredient  of  soils  that  under  ordinary  cir- 
cumstances exerts  a  considerable  surface  attraction  for 
ammonia  gas  is  clay.  Knop  examined  the  deportment  of 
ammonia  in  this  respect  towards  sand,  soluble  silica,  pure 
alumina,  carbonate  of  lime,  carbonate  of  magnesia,  hy- 
drated  sesquioxide  of  iron,  sulphate  of  lime,  and  humus. 

To  recapitulate,  the  soil  contains  carbonate  of  ammonia 
physically  absorbed  in  its  pores,  i.  e.,  adhering  to  the  sur- 
faces of  its  particles, — as  Knop  believes,  to  the  particles 
of  clay.  The  quantity  of  ammonia  is  variable  and  con- 
stantly varying,  being  increased  by  rain  and  dew,  or  ma- 
nuring, and  diminished  by  evaporation  of  water.  The 
actual  quantity  of  j^hysically  absorbed  ammonia  is,  in 
general,  very  small,  and  an  accurate  estimation  of  it  is, 
perhaps,  impracticable,  save  in  a  few  exceptional  cases. 

c.  Chemically  combined  AmmGnia. — The  reader  will 
have  noticed  that  in  the  experiments  of  Brustlein  just 
quoted,  a  greater  quantity  of  ammonia  was  absorbed  by 
the  soil  than  afterwards  escaped,  either  when  the  soil  was 
subjected  to  a  current  of  air  or  allowed  to  dry  after  moist- 
ening with  water.  This  ammonia,  it  is  therefore  to  be  be- 
lieved, was  in  great  part  retained  in  the  soil  in  chemical 
combination  in  the  form  of  compounds  that  not  only  do 
not  permit  it  readily  to  escape  as  gas,  but  also  are  not 
easily  washed  out  by  water.  The  bodies  that  may  unite 
with  ammonia  to  comparatively  insoluble  compounds  are, 
1st,  the  organic  acids  of  the  humus  group* — the  humus 
acids,  as  we  may  designate  them  collectively.  The  salts 
of  these  acids  have  been  already  noticed.     Their  com- 


*  Mulder  asserts  that  the  affinity  of  ulmic,  humic,  and  apocrenic  acids  for 
ammonia  is  so  strong  that  they  can  only  be  freed  from  it  hy  evaporation  of  their 
solutions  to  dryness  with  caustic  potash.  Boiling  with  carbonate  of  potash  or 
carbonate  of  soda  will  not  suffice  to  decompose  their  ammonia-salts.  We  hold 
it  more  likely  that  the  ammonia  which  requires  an  alkali  for  its  expulsion  is 
generated  by  the  decomposition  of  the  organic  acid  itself,  or,  if  that  be  desti- 
tute of  nitrogen,  of  some  nitrogenous  substance  admixed.  According  to  Bous- 
Bingault,  ammonia  is  completely  removed  from  humus  by  boiling  witii  water  and 
caustic  magnesia. 


244  HOW    CROPS    FEED. 

pounds  with  ammonia  are  freely  soluble  in  water;  hence 
strong  solution  of  ammonia  dissolves  them  from  the  soil. 
But  when  ammonia  salts  of  these  acids  are  put  in  contact 
with  lime,  magnesia,  oxide  of  iron,  oxide  of  manganese, 
and  alumina,  the  latter  being  in  jDreponderating  quantity, 
there  are  formed  double  compounds  which  are  insoluble 
or  slightly  soluble.  Since  the  humic,  ulmic,  crenic,  and 
apocrenic  acids  always  exist  in  soils  which  contain  organic 
remains,  there  can  be  no  question  that  these  double  salts  are 
a  chemical  cause  of  the  retention  of  ammonia  in  the  soil. 

2d.  Certain  phosphates  and  silicates  hereafter  to  be  no- 
ticed have  the  power  of  forming  difficultly  soluble  com- 
pounds with  ammonia. 

Reserving  for  a  subsequent  chapter  a  further  discussion 
of  the  causes  of  the  chemical  retention  of  ammonia  in  the 
soil,  we  may  now  appropriately  recount  the  observations 
that  have  been  made  regarding  the  condition  of  the  am- 
monia of  the  soil  as  regards  its  volatility,  solubility,  etc. 

Yolatility  of  the  Ammoiiia  of  the  Soil.  — We  have 
seen  that  ammonia  may  escape  from  the  soil  as  gaseous 
carbonate.  The  fact  is  not  only  true  of  this  substance  as 
physically  absorbed,  but  also  under  certain  conditions  of 
that  chemically  combined.  When  we  mingle  together 
equal  bulks  of  sulphate  of  lime  (gypsum)  and  carbonate 
of  ammonia,  both  in  the  state  of  fine  powder,  the  mixture 
begins  and  continues  to  smell  strongly  of  ammonia,  owing 
to  the  volatility  of  the  carbonate.  If  now  the  mixture  be 
drenched  with  water,  the  odor  of  ammonia  at  once  ceases 
to  be  perceptible,  and  if,  after  some  time,  the  mixture  be 
thrown  on  a  filter  and  washed  with  water,  we  shall  find 
that  what  remains  undissolved  contains  a  large  proportion 
of  carbonate  of  lime,  as  may  be  shown  by  its  dissolving 
in  an  acid  with  effervescence ;  wliile  the  liquid  that  has 
passed  the  filter  contains  sulphate  of  ammonia,  as  may  be 
learned  by  the  appropriate  chemical  tests  or  by  evaporat- 
ing to  dryness,  when  it  will  remain  as  a  colorless,  odorless. 


THE    AMMOXIA    OF    THE    SOIL.  245 

crystalline  solid.  Double  decomposition  has  taken  place 
between  the  two  salts  under  the  influence  of  water.  If, 
again,  the  carbonate  of  lime  on  the  filter  be  reunited  to 
the  liquid  filtrate  and  the  whole  be  evaporated,  it  will  be 
found  that  when  the  water  has  so  far  passed  ofi"  that  a 
moist,  pasty  mass  remains,  the  odor  of  ammonia  becomes 
evident  again — carbonate  of  ammonia,  in  fact,  escaping  by 
volatilization,  while  sulphate  of  lime  is  reproduced.  It  is 
a  general  law  in  chemistry  that  when  a  number  of  acids 
and  bases  are  together,  those  which  under  the  circum- 
stances can  produce  by  their  union  a  volatile  body  will 
unite,  and  those  which  under  the  circumstances  can  form  a 
solid  body  will  unite.  When  carbonic  and  sulphuric  acids, 
lime  and  ammonia,  are  in  mixture,  it  is  the  circumstances 
which  determine  in  what  mode  these  bodies  combine.  In 
presence  of  much  water  carbonate  of  lime  is  formed  be- 
cause of  its  insolubility,  water  not  being  able  to  destroy 
its  solidity,  and  sulphate  of  ammonia  necessarily  results 
by  the  union  of  the  other  two  substances.  When  the  wa- 
ter is  removed  by  evaporation,  all  the  possible  compounds 
between  carbonic  and  sulphuric  acids,  lime  and  am- 
monia, become  solid;  the  compound  of  ammonia  and  car- 
bonic acid  being  then  volatile,  this  fact  determines  its 
formation,  and,  as  it  escapes,  the  lime  and  sulphuric  acid 
can  but  remain  in  combination. 

To  apply  these  principles  :  When  carbonate  of  ammo- 
nia is  brought  into  the  soil  by  rain,  or  otherwise,  it  tends 
in  presence  of  much  water  to  enter  into  insoluble  combi- 
nations so  far  as  is  possible.  When  the  soil  becomes  dry, 
these  compounds  begin  to  undergo  decomposition,  provid- 
ed carbonates  of  lime,  magnesia,  potash,  and  soda,  are 
present  to  transpose  with  them ;  these  bases  taking  the 
place  of  the  ammonia,  while  the  carbonic  acid  they  were 
united  with,  forms  with  the  latter  a  volatile  compound. 
In  this  way,  then,  all  soils,  for  it  is  probable  that  no  soil 
exists  which  is  destitute  of  carbonates,  may  give  off  at  the 


246  HOY/    CSOPS    FSED. 

surface  in  dry  weather  a  portion  of  the  ammonia  which 
before  was  chemically  retained  within  it. 

Solubility  ©f  the  AmmoHia  of  the  Soil.— The  distinc- 
tions between  physically  adhering  and  chemically  combin- 
ed ammonia  are  difficult,  if  not  impossible,  to  draw  with 
accuracy.  In  what  follows,  therefore,  we  shall  not  attempt 
to  consider  them  separately. 

When  ammonia,  carbonate  of  ammonia,  or  any  of  the 
following  ammoniacal  salts,  viz.,  chloride,  sulphate,  ni- 
trate, and  phosphate,  are  dissolved  in  water,  and  the  solu- 
tions are  filtered  through  or  agitated  with  a  soil,  we  find 
that  a  portion  of  ammonia  is  invariably  removed  from  so- 
lution and  absorbed  by  the  soil.  An  instance  of  this  ab- 
sorbent action  has  been  already  given  in  recounting 
Brustlein's  experiments,  and  further  examples  will  be  here- 
after adduced  when  we  come  to  speak  of  the  silicates  of 
the  soil.  The  points  to  which  we  now  should  direct  at- 
tention are  these,  viz.,  1st,  the  soil  cannot  ahsorh  ammo- 
nia completely  from  its  solutions  ;  and,  2d,  the  ammonia 
ichich  it  does  ahsorh  may  he  to  a  great  degree  dissolved 
out  again  hy  water.  In  other  words,  the  compounds  of 
ammonia  that  are  formed  in  the  soil,  though  comparatively 
insoluble,  are  not  absolutely  so. 

Henneberg  and  Stohmann  found  that  a  light,  calcareous, 
sandy  garden  soil,  when  placed  in  twice  its  weight  of  pure 
water  for  24  hours,  yielded  to  the  latter  50^00  of  its  weight 
of  ammonia  (=0.0002"  |„). 

100  parts  of  the  same  soil  left  for  24  hours  in  200  parts 
of  a  solution  of  chloride  of  ammonium  (containing  2.182 
of  sal-ammoniac  =0.693  part  of  ammonia),  absorbed  0.112 
part  of  ammonia.  Half  of  the  liquid  was  j^oured  off 
and  its  place  supplied  with  j)ure  water,  and  the  whole 
left  for  24  hours,  w^hen  half  of  this  liquid  was  taken,  and 
the  process  of  dilution  was  thus  repeated  to  the  fifth  time. 
In  the  portions  of  Avater  each  time  removed,  ammonia  was 
estimated,  and  the  result  was  that  the  water  added  dis- 


THE    AMMOXIA    OF    THE    SOIL.    '  247 

solved  out  nearly  one-half  the  ammonia  wliicli  the  earth 

at  first  absorbed. 

The  1st  dilution  removed  from  tlie  soil  0.010 

"    2d        "  "  "      "      "  0.009 

"    3d        "  "  "      "      "  O.OM 

"    4tli      "  "  "      "      "  0.011 

*'    5th      "  ''  "      "      "  0.009 

Total 0.053 

Deducting  0.053  from  the  quantity  first  absorbed,  viz., 
0.112,  there  remains  0.059  part  retained  by  the  soil  after 
five  dilutions.  Knop,  in  11  decantations,  in  which  the 
soil  was  treated  with  8  times  its  weight  of  water,  removed 
93°  Iq  of  the  ammonia  which  the  soil  had  previously  ab- 
sorbed. We  cannot  doubt  that  by  repeating  the  washing 
sufficiently  long,  all  the  ammonia  would  be  dissolved, 
though  a  very  large  volume  of  water  would  certainly  be 
needful. 

Causes  which  ordinarily  prevent  the  Accumulation  ©f 
Ammonia  in  the  Soil. — The  ammonia  of  the  soil  is  con- 
stantly in  motion  or  suffering  change,  and  does  not  ac- 
cumulate to  any  great  extent.  In  summer,  the  soil  daily 
absorbs  ammonia  from  the  air,  receives  it  by  rains  and 
dews,  or  acquires  it  by  the  decay  of  vegetable  and  animal 
matters. 

Daily,  too,  ammonia  wastes  from  the  soil — by  volatili- 
zation— accompanying  the  vapor  of  water  which  almost 
unceasingly  escapes  into  the  atmosphere. 

When  the  soil  is  moist  and  the  temperature  not  too  low^, 
its  ammonia  is  also  the  subject  of  remarkable  chemical 
transformations.  Two  distinct  chemical  changes  are  be- 
lieved to  affect  it ;  one  is  its  oxidation  to  nitric  acid.'  This 
process  we  shall  consider  in  detail  in  the  next  section.  As 
a  result  of  it,  we  never  find  ammonia  in  the  water  of  or- 
dinary wells  or  deep  drains,  but  instead  always  encounter 
nitric  acid  united  to  lime,  and,  perhaps,  to  magnesia  and 
alkalies.  The  other  chemical  change  appears  to  be  the 
alteration  of  the  compounds  of  ammonia  with  the  humus 


248  HOW    CROPS    FEED. 

acids,  T^liereby  bodies  result  which  are  no  longer  soluble 
in  water,  and  which,  as  such,  are  probably  innutritions  to 
plants.  These  substances  are  quite  slowly  decomposed 
when  i^ut  in  contact,  especially  when  heated  with  alkalies 
or  caustic  lime  in  the  presence  of  water.  In  this  decom- 
position ammonia  is  reproduced.  These  indifferent  nitrog- 
enous matters  aj^pear  to  be  analogous  to  a  class  of  sub- 
stances known  to  chemists  as  amides^  of  which  asparagin, 
a  crystallizable  body  obtained  from  asparagus,  young  peas, 
etc.,  and  urea  and  uric  acid,  the  characteristic  ingredients 
of  urine,  are  examples.  Further  account  of  these  matters 
will  be  given  subsequently,  p.  276. 

Quantity  of  immonia  in  Soils. — Formerly  the  amount 
of  ammonia  in  soils  was  greatly  overestimated,  as  the  re- 
sult of  imperfect  methods  of  analysis.  In  1846,  Krocker, 
at  Liebig's  instigation,  estimated  the  nitrogen  of  22  soils, 
and  Liebig  published  some  ingenious  speculations  in  which 
all  this  nitrogen  was  incorrectly  assumed  to  be  in  the  form 
of  ammonia.  Later,  various  experimenters  have  attempt- 
ed to  estimate  the  ammonia  of  soils.  In  1855,  the  writer 
examined  several  soils  in  Liebig's  laboratory.  The  soils 
were  boiled  for  some  hours  with  water  and  caustic  lime, 
or  caustic  potash.  The  ammonia  that  was  set  free,  distill- 
ed off,  and  its  amount  was  determined  by  alkalimetry. 
It  was  found  that  however  long  the  distillation  was  kept 
up,  ammonia  continued  to  come  over  in  minute  quantity, 
and  it  was  probable  that  this  substance  was  not  simply 
exj^elled  from  the  soil,  but  was  slowly  formed  by  the  ac- 
tion of  lime  on  organic  matters,  it  being  well  known  to 
chemists  that  many  nitrogenous  bodies  are  thus  decom- 
posed.    The  results  were  as  follows : 


Ammonia. 
;  0.0169  p.ct. 
0.0186    " 


White  sandy  loam  distilled  with  caustic  lime    gave  iii  two  Exp's. 

^lowclay  ••         "  "         '    "         ".^«;™« 

"  "       potash    "      "    one      "       0.0075 

Black  garden  soil  "         "  "       lime        "      "    two       "     |  q  0953 


THE    AMMONIA    OF   THE    SOIL.  249 

The  fact  that  caustic  potash,  a  more  energetic  decom- 
posing agent  than  lime,  disengaged  more  ammonia  than 
the  latter  from  the  yellow  claj,  strengthens  the  Yiew  that 
ammonia  is  produced  and  not  merely  driven  off  under  the 
conditions  of  these  experiments,  and  that  accordingly  the 
figures  are  too  high.  Other  chemists  employing  the  same 
method  have  obtained  similar  results. 

Boussingault  (Agronomie,  T.  Ill,  p.  206)  was  the  first 
to  substitute  magnesia  for  potash  and  lime  in  the  estima- 
tion of  ammonia,  having  first  demonstrated  that  this  sub- 
stance, so  feebly  alkaline,  does  not  perceptibly  decompose 
gelatine,  albumin,  or  asparagine,  all  of  which  bodies,  espe- 
cially the  latter,  give  ammonia  when  boiled  with  milk  of 
lime  or  solutions  of  potash.  The  results  of  Boussingault 
here  follow. 

Localities.  Quantity  of  Ammonia  per  cent. 

Lie"bfranenberg,  Alsatia 0.0022 

Bischwiller,  "  0.0020 

Mei-ckwiller,  "         0.0011 

Bechelbronn,  "  0.0009 

Mittelhausbergen,  "  0.0007 

He  Napoleon,  Mulhouse, 0.0006 

Argentan,  Orne,  0.0060 

Quesnoy-sur-Deule,  Nord, 0.0012 

Eio  Madeira,  America,       0.0090 

Eio  Trombetto,  "  0.0030 

EioNegro,  "  0.0038 

Santarem,  "  0.0083 

IleduSalut,  "  0.0080 

Martinique,  "  0.0085 

Eio  Cupari,  (leaf  mold,)  " 0.0525 

Peat,  Paris,  0.0180 

The  above  results  on  French  soils  correspond  with  those 
obtained  more  recently  on  soils  of  Saxony  by  Knop  and 
Wolff,  who  have  devised  an  ingenious  method  of  estimat- 
ing ammonia,  which  is  founded  on  altogether  a  different 
principle.  Knop  and  Wolff  measure  the  nitrogen  gas 
which  is  set  free  by  the  action  of  chloride  of  soda  (Ja- 
velle  water*)  in  a  specially  constructed  apparatus,  the 

*  More  properly  hypocMorite  of  soda.,  -which,  is  used  in  mixture  with  bromine 
and  caustic  soda. 
11* 


250  HOW    CROPS    FEED. 

Azotometer.     {Chemisches  Gentralblatt^  1860,  pp.  243  and 
534.) 

By  this  method,  which  gives  accurate  results  when  ap- 
plied to  known  quantities  of  ammonia-salts,  Knop  and 
WoliF  obtained  the  following  results : 

Ammonia  in  dry  soil. 

Very  light  sandy  soil  from  bircli  forest 0.00077°  |o 

Eicli  lime  soil  from  beech  forest 0.00087 

Sandy  loam,  forest  soil 0.00012 

Forest  soil O.OOOSO 

Meadow  soil,  red  sandy  loam 0.00027 

Average 0.00056 

The  rich  alluvial  soils  from  tropical  America  are  ten  or 
more  times  richer  in  ready-formed  ammonia  than  those  of 
Saxony.  These  figures  show  then  that  the  substance  in 
question  is  very  variable  as  a  constituent  of  the  soil,  and 
that  in  the  ordinary  or  poorer  classes  of  unmanured  soils 
its  percentage  is  scarcely  greater  than  in  the  atmospheric 
waters. 

Tiie  Quantity  of  Amiii®ma  fluctuates.  — Boussingault 
has  further  demonstrated  by  analysis  what  we  have  insist- 
ed upon  already  in  this  chapter,  viz.,  that  the  quantity  of 
ammonia  is  liable  to  fluctuations.  He  estimated  ammonia 
in  garden  soil  on  the  4th  of  March,  1860,  and  then,  moist- 
ening two  samples  of  the  same  soil  with  pure  water,  ex- 
amined them  at  the  termination  of  one  and  two  months 
res^^ectively.     He  found, 

March  4th,  0.009°  \^  of  ammonia. 
April       "     0.014 
May        "     0.019 

The  simple  standing  of  the  moistened  soil  for  two 
months  sufficed  in  this  case  to  double  the  content  of  am- 
monia. 

The  quantitative  fluctuations  of  this  constituent  of  the 
soil  has  been  studied  further  both  by  Boussingault  and 
by  Knop  and  Wolfi".     The  latter  in  seeking  to  answer  the 


THE    NITRIC    ACID    OF    THE    SOIL.  251 

question — "  How  great  is  the  ammonia-content  of  good 
manured  soil  lying  fallow?" — made  repeated  determina- 
tions of  ammonia  (17  in  all)  in  tlie  same  soil  (well-ma- 
nured, sandy,  calcareous  loam  exposed  to  all  rains  and 
dews  but  not  washed)  during  five  months.  The  moist 
soil  varied  in  its  proportion  of  ammonia  with  the  greatest 
irregularity  between  the  extremes  of  0.0008  and  0.0003°  1^. 
Similar  observations  were  made  the  same  summer  on  the 
loamy  soil  of  a  field,  at  first  bare  of  vegetation,  then  cov- 
ered with  a  vigorous  potato  crop.  In  this  case  the  fluctu- 
ations ranged  from  0.0009  to  0.0003°  1^  as  irregularly  as  in 
the  other  instance. 

Knop  and  Wolff  examined  the  soil  last  mentioned  at 
various  depths.  At  3  ft.  the  proportion  of  ammonia  was 
scarcely  less  than  at  the  surface.  At  6  ft.  this  loam,  and 
at  a  somewhat  greater  depth  an  underlying  bed  of  sand, 
contained  no  trace  of  ammonia.  This  observation  ac- 
cords with  the  established  fact  that  deep  well  and  drain- 
waters  are  destitute  of  ammonia. 

Boussingault  has  discovered  {Agro7iomie^  3,  195)  that 
the  addition  of  caustic  lime  to  the  soil  largely  increases  its 
content  of  ammonia — an  effect  due  to  the  decomposing  ac- 
tion of  lime  on  the  amide-like  substances  already  noticed. 


§5. 


NITRIC  ACID  (NITRATES,  NITROUS  ACID,  AND  NITRITES)  OF 
THE  SOIL. 

Nitric  acid  is  formed  in  the  atmosphere  by  the  action 
of  ozone,  and  is  brought  down  to  the  soil  occasionally  in 
the  free  state,  but  almost  invariably  in  combination  with 
ammonia,  by  rain  and  dew,  as  has  been  already  described 
(p.  86).  It  is  also  produced  in  the  soil  itself  by  processes 
whose  nature — considerably  obscare  and  little  understood 
■ — will  be  discussed  presently. 


252  HOW    CEOPS    FEED. 

In  the  soil,  nitric  acid  is  always  combined  with  an 
alkali  or  alkali-earth,  and  never  exists  in  the  free  state  in 
appreciable  quantity.  We  speak  of  nitric  acid  instead  of 
nitrates,  because  the  former  is  the  active  ingredient  com- 
mon to  all  the  latter.  Before  considering  its  formation 
and  nutritive  relations  to  vegetation,  we  shall  describe 
those  of  its  compounds  which  may  exist  in  the  soil,  viz., 
the  nitrates  of  potash^  coda^  lime^  magnesia^  andiron. 

Nitrate  of  Potash  (K  NOJ  is  the  substance  com- 
mercially known  as  niter  or  saltpeter.  When  pure  (refin- 
ed saltpeter),  it  occurs  in  colorless  prismatic  crystals.  It 
is  freely  soluble  in  water,  and  has  a  peculiar  sharp,  cooling 
taste.  Crude  saltpeter  contains  common  salt  and  other 
imiDurities.  Nitrate  of  potash  is  largely  procured  for  in- 
dustrial uses  from  certain  districts  of  India  (Bengal)  and 
from  various  caves  in  tropical  and  temperate  climates,  by 
simply  leaching  the  earth  with  water  and  evaporating  the 
solution  thus  obtained.  It  is  also  made  in  artificial  niter- 
beds  or  plantations  in  many  European  countries.  It  is 
likewise  prepared  artificially  from  nitrate  of  soda  and 
caustic  potash,  or  chloride  of  potassium.  The  chief  use 
of  the  commercial  salt  is  in  the  manufacture  of  gunpowder 
and  fireworks. 

Sulphur,  charcoal,  (which  are  ingredients  of  gunpow- 
der), and  other  combustible  matters,  when  heated  in  con- 
tact with  a  nitrate,  burn  with  great  intensity  at  the  ex- 
pense of  the  oxygen  which  the  nitrate  contains  in  large 
proportion  and  readily  parts  with. 

Nitrate  of  Soda  (Na  NO3)  occurs  in  immense  quantities 
in  the  southern  extremity  of  Peru,  province  of  Tarapaca, 
as  an  incrustation  or  a  compact  stratum  several  feet  thick, 
on  the  pampa  of  Tamarugel,  an  arid  plain  situated  in  a 
region  where  rain  never  falls.  The  salt  is  dissolved  in  hot 
water,  the  solution  poured  off  from  sand  and  evaporated  to 
the  crystallizing  point.     The  crude  salt  has  in  general  a 


THE    NITEIC    ACID    OF    THE    SOIL.  253 

yellow  or  reddish  color.  When  pure,  it  is  white  or  color- 
less. From  the  shape  of  the  crystals  it  has  been  called 
cubic*  niter;  it  is  also  known  as  Chili  saltpeter,  having 
been  formerly  exported  from  Chilian  ports,  and  is  some- 
times termed  soda-saltpeter.  In  1854,  about  40,000  tons 
were  shipped  from  the  port  of  Iquique. 

N^itrate  of  soda  is  hygroscopic,  and  m  damp  air  be- 
comes quite  moist,  or  even  deliquesces,  and  hence  is  not 
suited  for  making  gunpowder.  It  is  easily  procured  arti- 
ficially by  dissolving  carbonate  of  soda  in  nitric  acid. 
This  salt  is  largely  employed  as  a  fertilizer,  and  for  pre- 
paring nitrate  of  potash  and  nitric  acid. 

Nitrate  of  Lime  {03.21^0^)  may  be  obtained  as  a  white 
mass  or  as  six-sided  crystals  by  dissolving  lime  in  nitric 
acid  and  evaporating  the  solution.  It  absorbs  water  from 
the  air  and  runs  to  a  liquid.  Its  taste  is  bitter  and  sharp. 
Nitrate  of  lime  exists  in  well-waters  and  accompanies 
nitrate  of  potash  in  artificial  niter-beds. 

Nitrate  of  Magacsia  (MgSNOg)  closely  resembles  ni- 
trate of  lime  in  external  characters  and  occurrence.  It 
may  be  prepared  by  dissolving  magnesia  in  nitric  acid  and 
evaporating  the  solution. 

Nitrates  of  Iroili — Various  compounds  of  nitric  acid 
and  iron,  both  soluble  and  insoluble,  are  known.  In  the 
soil  it  is  probable  that  only  insoluble  basic  nitrates  of 
sesquioxide  can  occur.  Knop  observed  ( VI  /St.,  V,  151) 
that  certain  soils  when  left  in  contact  with  solution  of  ni- 
trate of  potash  for  some  time,  failed  to  yield  the  latter  en- 
tirely to  water  again.  The  soils  that  manifested  this 
anomalous  deportment  were  rich  in  humus,  and  at  the 
same  time  contained  much  sesquioxide  of  iron  that  could 
be  dissolved  out  by  acids.  It  is  possible  that  nitric  acid 
entered  into  insoluble  combinations  here,  thouo:h  this 
hypothesis  as  yet  awaits  proof 

*  The  ciystals  are,  in  fact,  rhomboidal. 


o 


254  HOW    CKOFS    FEED. 

Mtrates  of  alumina  are  known  to  the  chemist,  but  have 
not  been  proved  to  exist  in  soils.  Nitrate  of  ammonia 
has  already  been  noticed,  p.  71. 

Nitric  Acid  a®t  usually  fixed  by  the  Soil. — In  its  deport- 
ment towards  the  soil,  nitric  acid  (either  free  or  in  its  salts) 
differs  in  most  cases  from  ammonia  in  one  important  j)ar- 
ticular.  The  nitrates  are  usually  not  fixed  by  the  soil,  but 
remain  freely  soluble  in  water,  so  that  washing  readily  and 
completely  removes  them.  The  nitrates  of  ammonia  and 
potash  are  decomposed  in  the  soil,  the  alkali  being  retain- 
ed, while  the  nitric  acid  may  be  removed  by  washing  with 
water,  mostly  in  the  form  of  nitrate  of  lime.  Mtrate  of 
soda  is  partially  decomposed  in  the  same  manner.  Free 
nitric  acid  unites  with  lime,  or  at  least  is  found  in  the 
washings  of  the  soil  in  combination  vvith  that  base. 

As  just  remarked,  Knop  has  observed  that  certain  soils 
containing  much  organic  matters  and  sesquioxide  of  iron, 
appeared  to  retain  or  decompose  a  small  portion  of  nitric 
acid  (put  in  contact  with  them  in  the  form  of  nitrate  of 
potash).  Knop  leaves  it  uncertain  whether  this  result  is 
simply  the  fault  of  the  method  of  estimation,  caused  by 
the  formation  of  basic  nitrate  of  iron,  which  is  insoluble  in 
water,  or,  as  is  perhaps  more  probable,  due  to  the  de- 
composing (reducing)  action  of  organic  matters. 

NitriUcation  is  the  formation  of  nitrates.  When  vege- 
table and  animal  matters  containing  nitrogen  decay  in  the 
soil,  nitrates  of  these  bases  presently  appear.  In  Bengal, 
during  the  dry  season,  when  for  several  months  rain  sel- 
dom or  never  falls,  an  incrustation  of  saline  matters, 
chiefly  nitrate  of  potash,  accumulates  on  the  surface  of 
those  soils,  which  are  most  fertile,  and  which,  though  culti- 
vated in  the  wet  season  only,  yield  two  and  sometimes 
three  crops  of  grain,  etc.,  yearly.  The  formation  of  ni- 
trates, which  probably  takes  place  during  the  entire  year, 
appears  to  go  on  most  rapidly  in  the  hottest  weather. 


THE    ISriTKIC    ACID    OF    THE    SOIL.  255 

The  nitrates  accumulate  near  the  surface  when  no  rain 
falls  to  dissolve  and  wash  them  down — when  evaporation 
causes  a  current  of  capillary  water  to  ascend  continually 
in  the  soil,  carrying  with  it  dissolved  matters  which  must 
remain  at  the  surface  as  the  water  escapes  into  the  atmos- 
phere. In  regions  where  rain  frequently  falls,  nitrates  are 
largely  formed  in  rich  soils,  but  do  not  accumulate  to  any 
extent,  unless  in  caves  or  positions  artificially  sheltered 
from  the  rain. 

Boussingault's  examination  of  garden  earth  from  Lieb- 
frauenberg  {Agronoonie^  etc.,  T.  II,  p.  10)  conveys  an  idea 
of  the  progress  which  nitrification  may  make  in  a  soil  un- 
der cultivation,  and  bighly  charged  with  nitrogenous  ma- 
nures. About  2.3  lbs.  of  sifted  and  well-mixed  soil  were 
placed  in  a  heap  on  a  slab  of  stone  under  a  glazed  roof. 
From  time  to  time,  as  was  needful,  the  earth  was  moist- 
ened with  water  exempt  from  ammonia.  The  proportion 
of  nitric  acid  was  determined  in  a  sample  of  it  on  the  day 
the  experiment  began,  and  the  analysis  Avas  repeated  four 
times  at  various  intervals.  The  subjoined  statement  gives 
the  per  cent  of  nitrates  expressed  as  nitrate  of  potash  in 
the  dry  soil,  and  also  the  quantity  of  this  salt  contained 
in  an  acre  taken  to  the  depth  of  one  foot.* 


Per  cent. 

Lbs. 

per  acre. 

857—  5th  August, 

0.01 

34 

"  — 17tli        '' 

0.06 

223 

"  —  2d  September, 

0.18 

634 

"  — 17tli        " 

0.23 

760 

"  —  2d  October, 

0.21 

738 

The  formation  of  nitrates  proceeded  rapidly  during  the 
heat  of  summer,  but  ceased  by  the  middle  of  September. 
Whether  this  cessation  was  due  to  the  lower  temperature 
or  to  the  complete  nitrification  of  all  the  matter  existing 
in  the  soil  capable  of  this  change,  or  to  decomposition 
of  nitric  acid  by  the  reducing  action  of  organic  matters, 


*  The  figures  given  above  are  abbreviated  from  the  originals,  or  reduced  to 
English  denominations  with  a  trifling  loss  of  exactness. 


256  HOW    CROPS    FEED. 

further  researches  must  decide.  The  quantities  that  ae- 
cumulated  in  this  experiment  are  seen  to  be  very  consider- 
able, when  we  remember  that  experience  has  shown  that 
200  lbs.  per  acre  of  the  nitrates  of  potash  or  soda  is  a 
large  dressing  upon  grain  or  grass.  Had  the  earth  been 
exposed  to  occasional  rain,  its  analysis  would  have  indi- 
cated a  much  less  percentage  of  nitrates,  because  the  salt 
would  have  been  washed  down  far  into,  and,  perhaps, 
out  of,  the  soil  but  no  less,  probably  even  somewhat 
more,  would  have  been  actually  formed.  In  August,  1856, 
Boussingault  examined  earth  from  the  same  garden  after  14 
days  of  hot,  dry  weather.  He  found  the  nitrates  equal  to 
911  lbs.  of  nitrate  of  potash  per  acre  taken  to  the  depth  of 
one  foot.  From  the  9th  to  the  29th  of  August  it  rained 
daily  at  Liebfrauenberg,  more  than  two  inches  of  water 
falling  during  this  time.  When  the  rain  ceased,  the  soil 
contained  but  38  lbs.  per  acre.  In  September,  rain  fell  15 
times,  and  to  the  amount  of  four  inches.  On  the  10th  of 
October,  after  a  fortnight  of  hot,  windy  weather,  the  gar- 
den had  become  so  dry  as  to  need  watering.  On  being 
then  analyzed,  the  soil  was  found  to  contain  nitrates  equiv- 
alent to  no  less  than  1,290  lbs.  of  nitrate  of  potash  per 
acre  to  the  depth  of  one  foot.  This  soil,  be  it  remembered, 
Avas  porous  and  sandy,  and  had  been  very  heavily  manur- 
ed with  well-rotted  compost  for  several  centuries. 

Boussingault  has  examined  more  than  sixty  soils  of  ev- 
ery variety,  and  in  every  case  but  one  found  an  apprecia- 
ble quantity  of  nitrates.  Knop  has  also  estimated  nitric 
acid  in  several  soils  (  Versuchs  jSt.,  Y,  143).  Nitrates  are 
almost  invariably  found  in  all  well  and  river  waters,  and 
in  quantities  larger  than  exist  in  rain.  "We  may  hence  as- 
sume that  nitrification  is  a  process  universal  to  all  soils, 
and  that  nitrates  are  normal,  though,  for  the  reasons  stat- 
ed, very  variable  ingredients  of  cultivated  earth. 

The  Sources  of  the  IVitric  Acid  which  is  formed  within 
the   Soil.— Nitric  acid  is  produced— a,  from  ammonia^ 


THE    NITRIC    ACID    OF    THE    SOIL.  257 

either  that  absorbed  by  the  soil  from  the  atmosphere,  or 
that  originating  in  the  soil  itself  by  the  decay  of  nitrog- 
enous organic  matters.  Knop  made  an  experiment  with 
a  sandy  loam,  as  follows :  The  earth  was  exposed  in  a  box 
to  the  vapor  of  ammonia  for  three  days,  was  then  mixed 
thoroughly,  spread  out  thinly,  moistened  with  pure  water, 
and  kept  sheltered  from  rain  until  it  became  dry  again. 
At  the  beginning  of  the  experiment,  1,000,000  parts  of 
the  earth  contained  52  parts  of  nitric  acid.  During  its 
exposure  to  the  air,  while  moist,  the  content-  of  nitric  acid 
in  this  earth  increased  to  591  parts  in  1,000,000,  or  more 
than  eleven  times ;  and,  as  Knop  asserts,  this  increase  took 
place  at  the  expense  of  the  ammonia  which  the  earth  had 
absorbed.  The  conversion  of  ammonia  into  nitric  acid  is 
an  oxidation  expressed  by  the  statement 

2  NH3  +  40  =  NH,  :N^03  +  11  fi.  - 
The  oxygen  may  be  either  ozone,  as  already  explained, 
or  it  may  be  furnished  by  a  substance  Avhich  exists  in  all 
soils  and  often  to  a  considerable  extent,  viz.,  sesquioxide 
of  iron.  This  compound  (Fe^  O3)  readily  yields  a  portion 
of  its  oxygen  to  bodies  which  are  inclined  to  oxidize,  be- 
ing itself  reduced  thereby  to  protoxide  (FeO)  thus: — 
Fe^  O3  =  2  FeO  +  O.  The  protoxide  in  contact  with  the 
air  quickly  absorbs  common  oxygen,  passing  into  sesqui- 
oxide again,  and  in  this  way  iron  operates  as  a  carrier  of 
atmospheric  oxygen  to  bodies  which  cannot  directly  com- 
bine with  the  latter.  The  oxidizing  action  of  sesquioxide 
of  iron  is  proved  to  take  place  in  many  instances  ;  for  ex- 
ample, a  rope  tied  around  a  rusty  iron  bolt  becomes  "  rot- 
ten," cotton  and  linen  fabrics  are  destroyed  by  iron-stains, 
the  head  of  an  iron  nail  corrodes  away  the  wood  sur- 
rounding it,  when  exposed  to  the  weather,  and  after  suf- 


*  The  above  equation  represents  but  one-half  of  the  ammonia  as  converted 
into  nitric  acid.  In  the  soil  the  carbonates  of  lime,  etc.,  would  separate  the 
nitric  acid  from  the  remaining  ammonia  and  leave  the  latter  in  a  condition  to 
be  oxidized. 


258  now  CROPS  feed. 

ficient  time  this  oxidation  extends  so  far  as  to  leave  the 
board  loose  upon  the  nail,  as  may  often  be  seen  on  old, 
unpainted  wooden  buildings.  Direct  experiments  by  Knop 
(  Ve7'suchs  /St.,  in,  228)  strongly  indicate  that  ammonia  is 
oxidized  by  the  agency  of  iron  in  tbe  soil. 

b.  The  organic  matters  of  tbe  soil,  either  of  vegetable 
or  animal  origin,  which  contain  nitrogen,  suffer  oxidation 
by  directly  combining  with  ordinary  oxygen. 

As  we  shall  presently  see,  nitrates  cannot  be  formed  in 
the  rapid  or  putrefactive  stages  of  decay,  but  only  later, 
when  the  process  proceeds  so  slowly  that  oxygen  is  in  large 
excess.  When  the  organic  matters  are  so  largely  dilut- 
ed or  divided  by  the  earthy  parts  of  the  soil  that  oxygen 
greatly  preponderates,  it  is  probable  that  the  nitrogen  of 
the  organic  bodies  is  directly  oxidized  to  nitric  acid. 
Otherwise  ammonia  is  first  formed,  which  is  converted  in- 
to nitrates  at  a  subsequent  slower  stage  of  decay. 

Nitrogenous  organic  matters  may  perhaps  likewise  yield 
nitric  acid  when  oxidized  by  the  intervention  of  hydrated 
sesquioxide  of  iron,  or  other  reducible  mineral  compounds. 
Thenard  mentions  i^Comptes  Rendus,  XLIX,  289)  that  a 
nitrogenous  substance  obtained  by  him  from  rotten  dung 
and  called  fumic  acid^  when  mixed  with  carbonate  of 
lime,  sesquioxide  of  iron  and  water,  and  kej)t  hot  for  15 
days  in  a  closed  vessel,  was  oxidized  with  formation  of 
carbonic  acid  and  noticeable  quantities  of  nitric  acid,  the 
sesquioxide  being  at  the  same  time  reduced  to  protoxide. 

The  various  sulphates  that  occur  in  soils,  especially  sul- 
phate of  lime  (gypsum,  plaster),  and  sulphate  of  iron 
(copperas),  may  not  unlikely  act  in  the  same  manner  to 
convey  oxygen  to  oxidable  substances.  These  sulphates, 
in  exclusion  of  air,  become  reduced  by  organic  matters  to 
sulphides.  This  often  happens  in  deep  fissures  in  the 
earth,  and  causes  many  natural  waters  to  come  to  the  sur- 


*  According  to  Mulder,  impure  humate  of  ammonia. 


THE    NITRIC    ACID    OF    THE    SOIL.  259 

face  cliarged  with  sulpliides  (sulphur-springs).  Water 
containing  sulphates  in  sohition  often  acquires  an  odor  of 
sulphuretted  hydrogen  by  being  kept  bottled,  the  cork  or 
other  organic  matters  deoxidizing  the  sulphates.  The 
earth  just  below  the  paving-stones  in  Paris  contains  con- 
siderable quantities  of  sulphides  of  iron  and  calcium,  the 
gypsum  in  the  soil  being  reduced  by  organic  matters. 
(Chevrenl.)  These  sulphides,  when  exposed  to  air,  speed- 
ily oxidize  to  sulphates,  to  suffer  reduction  again  in  con- 
tact with  the  appropriate  substances,  and  under  certain 
conditions,  operate  continuously,  to  gather  and  impart 
oxygen.  One  of  the  causes  of  the  often  remarkable  and 
inexplicable  effects  of  plaster  of  Paris  when  used  as  a  fer- 
tilizer may,  perhaps,  be  traced  to  this  power  of  oxidation, 
resulting  in  the  formation  of  nitrates.  This  point  requires 
and  is  well  worthy  of  special  investigation. 

c.  Lastly,  the  free  nitrogen  of  the  atmosphere  appears 
to  be  in  some  way  involved  in  the  act  of  nitrification — is 
itself  to  a  certain  extent  oxidized  in  the  soil,  as  has  been 
maintained  by  Saussure,  Gaultier  de  Claubry,  and  others 
{Gmelhi's  Sand-booh  of  Chemistry^  II,  388). 

The  truth  of  this  view  is  sustained  by  some  of  Bous- 
singault's  researches  on  the  garden  soil  of  Liebfrauenberg 
{Agrono7nie,  etc.,  T.,  1,  318).  On  the  29th  of  July,  1858, 
he  spread  out  thinly  120  grammes  of  this  soil  in  a  shallow 
glass  dish,  and  for  three  months  moistened  it  daily  with 
water  exempt  from  compounds  of  nitrogen.  At  the  end 
of  this  time  analysis  of  the  soil  showed  that  while  a  small 
proportion  of  carbon  (0.825°  |„)  had  wasted  by  oxidation, 
the  quantity  of  nitrogen  had  slightly  increased.  The 
gain  of  nitrogen  was  but  0.009  grm.  =  0.008°|  ^. 

In  five  other  experiments  where  plants  grew  for  several 
months  in  small  quantities  of  the  same  garden  soil,  either 
in  the  free  air  but  sheltered  from  rain  and  dew,  or  in  a 
confined  space  and  watered  with  pure  waiter,  analyses 


260  HOW    CROPS    FEED. 

were  made  of  the  soil  and  seed  before  the  trial,  and  of  the 
soil  and  crop  afterwards. 

The  analyses  show  that  while  in  all  cases  the  plants 
gained  some  nitrogen  beyond  what  was  originally  contain- 
ed in  the  seed,  there  was  in  no  instance  any  loss  of  nitro- 
gen by  the  soil,  and  in  three  cases  the  soil  contained  more 
of  this  element  after  than  before  the  trial.  Here  follow 
the  results. 


No.  of  Exp. 

Weight  of  Crop, 
the  seed  taken  as  1. 

Quantity  of  Soil. 

Gain  of 

Nitrogen 

by  plant. 

by  soil. 

1.  Lupin,* 

31/2 

130  grms. 

0.0042  grms. 

0.0672  grms. 

2.  Lupin, 

4 

130      " 

0.0047      " 

0.0081      " 

3,  Hemp, 

5 

40      " 

0.0039      " 

0.0000      " 

4.  Bean, 

5 

50      " 

0.0226      " 

0.0000      " 

5.  Lupin,* 

8 

130      " 

0.0217      " 

0.0454      " 

That  the  gain  of  nitrogen  by  the  soil  was  not  due  to 
direct  absorption  of  nitric  acid  or  ammonia  from  the  at- 
mosphere is  demonstrated  by  the  fact  that  it  was  largest 
in  the  two  cases  (Exps.  1  and  5)  where  the  experiment  was 
conducted  in  a  closed  ressel,  containing  throughout  the 
whole  time  the  same  small  volume,  about  20  gallons,  of 
air. 

In  Exp.  4,  where  the  soil  at  the  conclusion  contained  no 
more  nitrogen  than  at  the  commencement  of  the  trial,  it 
is  scarcely  to  be  doubted  that  the  considerable  gain  of  ni- 
trogen experienced  by  the  plant  came  through  the  soil, 
and  would  have  been  found  in  the  latter  had  it  borne  no 
crop. 

The  experiments  show  that  the  quantity  of  nitrogen 
assimilated  from  the  atmosphere  by  a  given  soil  is  very 
variable,  or  may  even  amount  to  nothing  (Exp.  3);  but 
they  give  us  no  clue  to  the  circumstances  or  conditions 
which  quantitatively  influence  the  result.  It  must  be  ob- 
served that  this  fixation  of  nitrogen  took  place  here  in  a 
soil  very  rich  in  organic  matters,  existing  in  the  condition 
of  humus,  and  capable  of  oxidation,  so  that  the  soil  itself 

*  Experiments  made  in  confined  air. 


THE   NITRIC    ACID    OF    THE    SOIL.  261 

lost  during  three  summer  months  eight-tenths  of  one  per 
cent  of  carbon.  In  the  numerous  similar  experiments 
made  by  Boussingault  with  soils  destitute  of  organic  mat- 
ter^ no  accumulation  of  nitrogen  occurred  beyond  the 
merest  traces  coming  from  condensation  of  atmospheric 
ammonia. 

Certain  experiments  executed  by  Mulder  more  than  20 
years  ago  ( Chemistry  of  Animal  and  Vegetable  Physi- 
ology, p.  673)  confirm  the  view  we  have  taken.  Two  of 
these  were  "made  with  beans  which  had  germinated  in 
an  atmosphere  void  of  ammonia,  and  grown,  in  one  case, 
in  ulmic  acid  prepared  from  sugar,  and  also  free  from  am- 
monia; and,  in  the  other  case,  in  charcoal,  both  being 
moistened  with  distilled  water  free  from  ammonia.  The 
ulmic  acid  and  the  charcoal  were  severally  mixed  up  with 
1  per  cent  of  wood  ashes,  to  supply  the  plants  with  ash- 
ingredients.  I  determined  the  proportion  of  nitrogen  in 
three  beans,  and  also  in  the  plants  that  were  produced  by 
three  other  beans.     The  results  are  as  follows : — 

WMte  beans  in  ulmic  acid.  Brown  beans  in  charcoal. 

Weight.  Nitrogen.  Weight.  Nitrogen. 

Beans,  1.465  gnn.  50  cub.  cent.  1.277  27  cub.  cent. 

Plants,  4.167    "  160    '^       "  1.772  54    " 

The  white  beans,  therefore,  whilst  growing  into  plants 
in  substances  and  an  atmosphere,  both  of  which  were  free 
of  ammonia,  had  obtained  more  than  thrice  the  quantity 
of  nitrogen  that  originally  existed  in  the  beans ;  in  the 
brown  beans  the  original  quantity  was  doubled."  Mulder 
believed  this  experiment  to  furnish  evidence  that  ammonia 
is  produced  by  the  union  of  atmospheric  nitrogen  with 
hydrogen  set  free  in  the  decay  of  organic  matters.  To 
this  notion  allusion  has  been  already  made,  and  the  con- 
viction expressed  that  no  proof  can  be  adduced  in  its 
favor  (p.  239).  The  results  of  the  experiments  are  fully 
explained  by  assuming  that  nitrogen  was  oxidized  in  nitri- 
fication, and  no  other  explanation  yet  proposed  accords 
with  existingr  facts. 


262  HOW    CEOPS    FEED. 

As  to  the  mode  in  wliich  the  soil  thus  assimilates  free 
nitrogen,  several  hypotheses  have  been  offered.  One  is 
that  of  Schonbein,  to  the  effect  that  in  the  act  of  evapora- 
tion free  nitrogen  and  water  combine,  with  formation  of 
nitrite  of  ammonia.  In  a  former  paragraph,  p.  79,  we 
have  given  the  results  of  Zabelin,  which  appear  to  render 
this  theory  inadmissible. 

A  second  and  adequate  explanation  is,  that  free  nitrogen 
existing  in  the  cavities  of  the  soil  is  directly  oxidized  to 
nitric  acid  by  ozone,  which  is  generated  in  the  action  of 
ordinary  oxygen  on  organic  matters,  (in  the  same  way  as 
happens  when  ordinary  oxygen  acts  on  phosphorus,)  or  is, 
perhaps,  the  result  of  electrical  disturbance. 

Experiments  by  Lawes,  Gilbert,  and  Pugh  {Phil. 
Trans.,  1861,  II,  495),  show  indeed  that  organic  matters 
in  certain  conditions  of  decay  do  not  yield  nitric  acid 
under  the  influence  of  ozone. 

They  caused  air  highly  impregnated  with  ozone  to  pass 
daily  for  six  months  through  moist  mixtures  of  burned 
soil  with  relatively  large  quantities  of  saw-dust,  starch, 
and  bean  meal,  with  and  without  lime — in  all  10  mixtures 
— but  in  no  case  was  any  nitric  acid  produced. 

It  would  thus  appear  that  ozone  can  form  nitrates  in 
the  soil  only  when  organic  matters  have  passed  into  the 
comparatively  stable  condition  of  humus. 

That  nitrogen  is  oxidized  in  the  soil  by  ozone  is  highly 
probable,  and  in  perfect  analogy  with  what  must  happen 
in  the  atmosphere,  and  is  demonstrated  to  occur  in  Schon- 
bein's  experiments  with  moistened  phosphorus  (p.  QQ, 
also  Ann.  der  Chem.  u.  Pharm.,  89,  287),  as  well  as  in 
Zabelin's  investigations  that  have  been  already  recounted. 
(See  pp.  75-83.) 

he  fact,  established  by  Reichardt  and  Blumtritt,  that 
humus  condenses  atmospheric  nitrogen  in  its  pores  (p. 
167),  doubtless  aids  the  oxidation  of  this  element. 

The  third  mode  of  accounting  for  the  oxidation  of 


THE    NITfilC    ACID    OF    THE    SOIL.  263 

free  nitrogen  is  based  upon  the  effects  of  a  reducible 
body,  like  sesquioxide  of  iron  or  sulphate  of  lime,  to 
which  attention  has  been  already  directed. 

In  a  very  carefully  conducted  experiment,  Cloez  *  trans- 
mitted atmospheric  air  purified  from  suspended  dust,  and 
from  nitric  acid  and  ammonia,  through  a  series  of  10  large 
glass  vessels  filled  with  various  porous  materials.  Vessel 
No.  1  contained  fragments  of  unglazed  porcelain ;  "No,  2, 
calcined  pumice-stone ;  ^N'o.  3,  bits  of  well-washed  brick. 
Each  of  these  three  vessels  also  contained  10  grms.  of  car- 
bonate of  potash  dissolved  in  water.  The  next  three  vessels, 
Kos.  4, 5,  and  6,  included  the  above-named  porous  materials 
in  the  same  order ;  but  instead  of  carbonate  of  potash,  they 
were  impregnated  with  carbonate  of  lime  by  soaking  in 
water,  holding  this  compound  in  suspension.  The  vessel 
N'o.  7  was  occupied  with  Meudon  chalk,  washed  and 
dried.  ISTo.  8  contained  a  clayey  soil  thoroughly  washed 
with  water  and  ignited  so  as  to  carbonize  the  organic 
matters  without  baking  the  clay.  ISTo.  9  held  the  same 
earth  washed  and  dried,  but  not  calcined.  Lastly,  in  'No. 
10,  was  placed  moist  pumicfe-stone  mixed  with  pure  car- 
bonate of  lime  and  10  grms.  of  urea,  the  nitrogenous  princi- 
ple of  urine.  Through  these  vessels  a  slow  stream  of  puri- 
fied air,  amounting  to  160,000  liters,  was  passed,  night  and 
day,  for  8  months.  At  the  conclusion  of  the  experiment, 
vessel  No.  1  contained  a  minute  quantity  of  nitric  acid, 
which,  undoubtedly,  came  from  the  atmosphere,  having 
escaped  the  purifying  apparatus.  The  contents  of  Xos. 
2,  4,  and  5,  were  free  from  nitrates.  Nos.  3  and  .6,  con- 
taining fragments  of  washed  brick,  gave  notable  evidences 
of  nitric  acid.  Traces  were  also  found  in  the  washed 
chalk.  No.  7,  and  in  the  calcined  soil,  ISTo.  8.  In  N'o.  9, 
filled  with  washed   soil,   niter  was   abundant.     ISTo.   10, 


*  Recherches  sur  la  Nitrification— Legons  de  Chimie  profess6es  en  1861  a  la 
Socif^te  Chimique  de  Paris,  pp.  145-150. 


264         .  HOW    CROPS    FEED. 

containing  pumice,  carbonate  of  lime,  and  urea,  was  desti- 
tute of  nitrates. 

Experiments  2, 4,  and  5,  demonstrate  that  the  concourse 
of  nitrogen  gas,  a  jDorous  body,  and  an  alkali-carbonate, 
is  insufficient  to  j)roduce  nitrates.  Experiment  Ko.  10 
shows  that  the  highly  nitrogenous  substance,  urea,"  dif- 
fused throughout  an  extremely  porous  m.edium  and  expos- 
ed to  the  action  of  the  air  in  moist  contact  with  carbonate 
of  lime,  does  not  suffer  nitrification.  In  the  brick  (ves- 
sels Nos.  3  and  6),  something  was  obviously  present, 
which  determined  the  oxidation  of  free  atmospheric  ni- 
trogen. Cloez  took  the  brick  fresh  from  the  kiln  where 
it  was  burned,  and  assured  himself  that  it  included  at 
the  beginning  of  the  experiment,  no  nitrogen  in  organic 
combination  and  no  nitrates  of  any  kind.  Cloez  believes 
the  brick  to  have  contained  some  oxidable  mineral  sub- 
stance, probably  sulphide  of  iron.  The  Gentilly  clay, 
used  in  making  the  brick,  as  well  as  some  iron-cinder, 
added  to  it  in  the  manufacture,  furnished  the  elements  of 
this  compound. 

The  slight  nitrification  that  occurred  in  the  vessels 
ISTos.  7  and  8,  containing  washed  chalk  and  burned  soil, 
likewise  points  to  the  oxidizing  action  of  some  mineral 
matter.  In  vessel  N'o.  9,  the  simply  washed  soil,  which 
was  thus  freed  from  nitrates  before  the  trial  began,  un- 
derwent a  decided  nitrification  in  remarkable  contrast  to 
the  same  soil  calcined  (No.  8).  The  influence  of  humus 
is  thus  brought  out  in  a  striking  manner. 

It  may  be  that  apocrenic  acid,  which  readily  yields 
oxygen  to   oxidable  matters,  is  an  important  agent  in 


Urea  (COH4  No)  contains  in  100  parts  : 

Carbon,  20.00 
Hydrogen,  6.67 
Nitrogen,  46.67 
Oxygen,        26.66 


100.00 


THE   K"ITKIC    ACID    OP    THE    SOIL.  265 

nitrification.  As  we  have  seen,  this  acid,  according  to 
Mulder,  passes  into  crenic  acid  by  loss  of  oxygen,  to  be 
reproduced  from  the  latter  by  absorption  of  free  oxygen. 
The  apocrenate  of  sesquioxide  of  iron,  in  which  both  acid 
and  base  are  susceptible  of  this  transfer  of  oxygen, 
should  thus  exert  great  oxidizing  power.     (See  p.  228.) 

The  Conditions  Influencing  Nitrification  have  been 
for  the  most  part  already  mentioned  incidentally.  We 
may,  however,  advantageously  recapitulate  them. 

a.  The  formation  of  nitrates  appears  to  require  or  to  be 
facilitated  by  an  elevated  temperature^  and  goes  on  most 
rapidly  in  hot  weather  and  in  hot  climates. 

h.  According  to  Knop,  ammonia  that  has  been  absorbed 
by  a  soil  suffers  no  change  so  long  as  the  soil  is  dry ;  but 
when  the  soil  is  moistened,  nitrification  quickly  ensues. 
Water  thus  appears  to  be  indispensable  in  this  process. 

c.  An  alkali  base  or  carbonate  appears  to  be  essential 
for  the  nitric  acid  to  combine  with.  It  has  been  thought 
that  the  mere  presence  of  potash,  soda,  and  lime,  favors 
nitrification,  "  disposes,"  as  is  said,  nitrogen  to  unite  with 
oxygen.  Boussingault  found,  however  {Chimie  Agri- 
cole^  III,  198),  that  caustic  lime  developed  ammonia  from 
the  organic  matters  of  his  garden  soil  without  favoring 
nitrification  as  much  as  mere  sand.  The  caustic  lime  by 
its  chemical  action,  in  fact,  opposed  nitrification ;  while 
pure  sand,  probably  by  dividing  the  particles  of  earth  and 
thus  perfecting  their  exposure  to  the  air,  facilitated  this 
process.  Boussingault's  experiments  on  this  point  were 
made  by  inclosing  an  earth  of  known  composition  (from  his 
garden)  with  sand,  etc.,  in  a  large  glass  vessel,  and,  after 
three  to  seven  months,  analyzing  the  mixtures,  which  were 
made  suitably  moist  at  the  outset.  Below  are  the  results 
of  five  experiments. 

I.  1000  grms.  of  soil  and  850  grms.  sand  acquired  0.012  grms.  ammonia  and 
0.482  grms.  nitric  acid. 

IT.  1000  grms.  of  soil  and  5500  grms.  sand  acquired  0.035  grms.  ammonia  and 
0.545  grms.  nitric  acid. 

12 


266  HOW    CROPS    FEED. 

m.  1000  grms.  of  soil  and  500  grms.  marl  acquired  0.002  grms.  ammonia  and 
0.360  grms.  nitric  acid. 

IV.  1000  grms.  of  soil  and  2  grms.  carbonate  of  potash  acquired  0.015  grms, 
ammonia  and  0.290  grms.  nitric  acid. 

V.  1000  grms.  of  soil  and  200  grms.  quicklime  acquired  0.303  grms.  ammonia 
and  0.099  grms.  nitric  acid. 

The  unfaYorable  effect  of  caustic  lime  is  well  pronounc- 
ed and  is  confirmed  by  other  similar  experiments.  Car- 
bonate of  ]3otasli,  which  is  strongly  alkaline,  but  was  used 
in  small  quantity,  and  marl  (carbonate  of  lime),  which  is 
but  very  feebly  alkaline,  are  plainly  inferior  to  sand  in 
their  influence  on  the  development  of  nitric  acid. 

The  effect  of  lime  or  carbonate  of  potash  in  these  ex- 
periments of  Boussingault  may,  perhaps,  be  thus  explain- 
ed. Many  organic  bodies  which  are  comparatively  stable 
of  themselves,  absorb  oxygen  with  great  avidity  in  pres- 
ence of,  or  rather  when  combined  with,  a  caustic  alkali. 
Crenic  acid  is  of  this  kind ;  also  gallic  acid  (derived  from 
nut-galls),  and  especially  pyrogallic  acid  (a  result  of  the 
dry  distillation  of  gallic  acid).  The  last-named  body, 
when  dissolved  in  potash,  almost  instantly  removes  the 
oxygen  from  a  limited  volume  of  air,  and  is  hence  used 
for  analysis  of  the  atmosphere.* 

We  reason,  then,  that  certain  organic  matters  in  the 
soil  of  Boussingault's  garden,  became  so  altered  by  treat- 
ment with  lime  or  carbonate  of  potash  as  to  be  susceptible 
of  a  rapid  oxidation,  in  a  manner  analogous  to  what  hap- 
pens with  pyrogallic  acid.  Dr.  R.  Angus  Smith  has  shown 
{Jour.  Moy.  Ag.  Soc,  XYII,  436)  that  if  a  soil  rich  in  or- 
ganic matter  be  made  alkaline,  moist,  and  warm,  putre- 
fictive  decomposition  may  shortly  set  in.  This  is  what 
happens  in  every  well-managed  compost  of  lime  and  peat. 
By  this  rapid  alteration  of  organic  matters,  as  we  shall  see 
(p.  268),  not  only  is  nitric  acid  not  formed,  but  nitrates 
added  are  reduced  to  ammonia.     It  is  not  improbable  that 


*  Not  all  organic  bodies,  by  any  means,  are  thus  affected.     Lime  hinders  the 
alteration  of  urine,  flesh,  and  the  albuminoids. 


THE    KITEIC    ACID    OF    THE    SOIL.  267 

smaller  doses  of  lime  or  alkali  than  those  employed  by 
Boussingault  would  have  been  found  promotive  of  nitri- 
fication, especially  after  the  lapse  of  time  sufficient  to 
allow  the  first  rapid  decomposition  to  subside,  for  then 
we  should  expect  that  its  presence  would  favor  slow  oxida- 
tion. This  view  is  in  accordance  with  the  idea,  universally 
received,  that  hme,  or  alkali  of  some  sort,  is  an  indispensa- 
ble ingredient  of  artificial  niter-beds.  The  point  is  one 
upon  which  further  investigations  are  needed. 

d.  Free  oxygen^  i.  e.,  atmospheric  air,  and  the  porosity 
of  soil  Tv^hich  ensures  its  contact  with  the  particles  of  the 
latter,  are  indispensable  to  nitrification,  which  is  in  all 
cases  a  process  of  oxidation.  When  sesquioxide  of  iron 
oxidizes  organic  matters,  its  action  would  cease  as  soon  as 
its  reduction  to  protoxide  is  complete,  but  for  the  atmos- 
pheric oxygen,  which  at  once  combines  with  the  protoxide, 
constantly  reproducing  the  sesquioxide. 

In  the  saltpeter  plantations  it  is  a  matter  of  experience 
that  light,  porous  soils  yield  the  largest  product.  The 
operations  of  tillage,  which  promote  access  of  air  to  the 
deeper  portions  of  earth  and  counteract  the  tendency  of 
many  soils  to  "  cake  "  to  a  comparatively  impervious  mass, 
must  also  favor  the  formation  of  nitrates. 

Many  authors,  especially  Mulder,  insist  upon  the  physic- 
al influence  of  porosity  in  determining  nitrification  by 
condensed  oxygen.  The  probability  that  porosity  may 
assist  this  process  where  compounds  of  nitrogen  are  con- 
cerned, is  indeed  great ;  but  there  is  no  evidence  that  any 
porous  body  can  determine  the  union  of  free  nitrogen  and 
oxygen.  Knop  found  that  of  all  the  proximate  ingredi- 
ents of  the  soil,  clay  alone  can  be  shown  to  be  capable  of 
physically  condensing  gaseous  ammonia  (humus  combines 
with  it  chemically,  and  if  it  previously  efiects  physical 
condensation,  the  fact  cannot  be  demonstrated). 

The  observations  by  Keichardt  and  Blumtritt  on  the 
condensing  effect  of  the  soil  for  the  erases  of  the  atmos- 


268  now  CROPS  feed. 

phere  (p.  167)  indicate  absorption  both  of  oxygen  and 
nitrogen,  as  well  as  of  carbonic  acid.  The  fact  that  char- 
coal acts  as  an  energetic  oxidizer  of  organic  matters  has 
been  alluded  to  (p.  169).  This  action  is  something  very 
remarkable,  although  charcoal  condenses  oxygen  but  to  a 
slight  extent.  The  soil  exercises  a  similar  but  less  vigorous 
oxidizing  effect,  as  the  author  is  convinced  from  experi- 
ments made  imder  his  direction  (by  J.  J.  Matthias,  Esq.), 
and  as  is  to  be  inferred  from  the  well-known  fact  that  the 
odor  of  putrefying  flesh,  etc.,  cannot  pass  a  certain  thickness 
of  soil.  But  charcoal  is  unable  to  accomplish  the  union 
of  oxygen  and  nitrogen  at  common  temperatures,  or  afc 
212°  F.,  either  dry,  moistened  with  pure  water,  or  with 
solution  of  caustic  soda.  (Experiments  in  Sheffield  labo- 
ratory, by  Dr.  L.  H.  Wood.) 

Putrefying  flesh,  covered  with  charcoal  as  in  Stenhouse's 
experiment  (p.  169)  gives  off  ammonia,  but  no  nitric  acid  is 
formed.  Dumas  has  indeed  stated  ( Comptes  Mend.^  XXIII) 
that  ammonia  mixed  with  air  is  converted  into  nitric 
acid  by  a  porous  body — chalk— that  has  been  drenched 
with  caustic  potash  and  is  heated  to  212°  F.  But  this  is 
an  error,  as  Dr.  Wood  has  demonstrated.  It  is  true  that 
platinum  at  a  high  temperature  causes  ammonia  and  oxy- 
gen to  unite.  Even  a  platinum  wire  when  heated  to  red- 
ness exerts  this  effect  in  a  striking  manner  (Kraut,  A^in. 
Ch.  11.  PA.,  136,  69) ;  but  spongy  platinum  is  without  ef- 
fect on  a  mixture  of  air  and  ammonia  gas  at  212°  or  lower 
temperatures.     (Wood.) 

e.  Presence  of  organic  raatters  prone  to  oxidation.  He- 
duction  of  nitrates  to  ammonia^  etc.^  in  the  soil.^As  wc 
have  seen,  the  organic  matters  (humus)  of  the  soil  are  a 
source  of  nitric  acid.  But  it  appears  that  this  is  not  al- 
ways or  universally  true.  In  compact  soils,  at  a  certain 
depth,  organic  matters  (their  hydrogen  and  carbon)  may 
oxidize  at  the  expense  of  nitric  acid  itself,  converting  the 
latter  into  ammonia.     Pelouze  (Oomptes  Mendus^  XLIY, 


THE    IflTEIC    ACID    OF   THE    SOIL.  2B9 

118)  has  proved  that  putrefying  animal  substances,  as  al- 
bumin, thus  reduce  nitric  acid  with  formation  of  ammonia. 
For  this  reason,  he  adds,  the  liquor  of  dung  heaps  and 
putrid  urine  contains  little  or  no  nitrates.  Boussingault 
{^Agronomie^  II,  17)  examined  a  remarkably  rich  alluvial 
soil  from  the  junction  of  the  Amazon  with  the  Rio  Cu^^ari, 
made  up  of  alternate  layers  of  sand  and  partially  decayed 
leaves,  containing  40^  |o  of  the  latter.  This  natural  leaf- 
compost  contained  no  trace  of  nitrates,  but  an  exception- 
ally high  quantity  of  ammonia,  viz.,  .05°  |g. 

Kuhlmann  [Ann.  de  Chim.  et  d&  Fhys.,  3  Ser.,  XX) 
was  the  first  to  draw  attention  to  the  probability  that  ni- 
tric acid  may  thus  be  deoxidized  in  the  lower  strata  of 
the  soil,  and  his  arguments,  drawn  from  facts  observed 
in  the  laboratory,  appear  to  apply  in  cases  where  there 
exist  much  organic  matters  and  imperfect  access  of  air. 
In  a  soil  so  porous  as  is  demanded  for  the  culture  of  most 
crops  these  conditions  cannot  usually  occur,  as  Grouven 
has  taken  the  trouble  to  demonstrate  {Zeitschrift  far 
Deutsche  LandwirtJie^  1855,  p.  341).  In  rice  swamps  and 
peat  bogs,  as  well  as  in  wet  compost  heaps,  this  reduction 
must  proceed  to  a  considerable  extent. 

In  some,  if  not  all  cases,  the  addition  of  much  lime  or 
other  alkaline  substance  to  a  soil  rich  in  organic  matters 
sets  up  rapid  putrefactive  decomposition,  whereby  nitrates 
are  at  once  reduced  to  ammonia  (p.  266). 

In  one  and  the  same  soil  the  conditions  may  exist  at 
difierent  times  that  favor  nitrification  on  the  one  hand, 
and  reduction  of  nitrates  to  ammonia  on  the  other.  A 
surplus  of  moisture  might  so  exclude  air  from  a  porous 
soil  as  to  cause  reduction  to  take  place,  to  be  succeeded 
by  rapid  nitrification  as  the  soil  becomes  more  dry. 

It  is  possible  that  nitrates  may  undergo  further  chemi- 
cal alteration  in  the  presence  of  excess  of  organic  matters. 
That  nitrites  may  often  exist  in  the  soil  is  evident  from 
what  has  been  written  with  reorard  to  the  mutual  convert- 


2T0  HOW    CROPS    FEED. 

ibility  of  nitrates  and  nitrites  (p.  73).  According  to 
Goppelsruder  {p'mgler's  Poly  tech.  Jour.^  164,  388),  ce?'tain 
soils  rich,  in  humus  possess  in  a  high  degree  the  |)Ower  to 
reduce  nitrates  to  nitrites.  It  is  not  unlikely  that  further 
reduction  may  occur — that,  in  fact,  the  deoxidation  may 
be  complete  and  free  nitrogen  be  disengaged.  This  is  a 
question  eminently  "worthy  of  study. 

Loss  of  Nitrates  may  occur  when  the  soil  is  saturated  j 
with  water,  so  that  the  latter  actually  flows  through  and 
away  from  it,  as  happens  during  heavy  rains,  the  nitrates 
(those  of  sesquioxide  of  iron,  perhaps,  excepted)  being 
freely  soluble  and  not  retained  by  the  soil.  Boussiugault 
made  40  analyses  of  lake  and  river  water,  25  of  spring 
water,  and  35  of  well  water,  and  found  nitric  acid  in  ev- 
ery case,  though  the  quantity  varied  greatly,  being  largest 
in  cities  and  fertile  regions.  Thus  the  water  of  the  upper 
Hhine  contains  one  millionth,  that  of  the  Seine,  in  Paris, 
six  millionth s,  and  that  of  the  N^ile  four  millionths  of  ni- 
tric acid.  The  Rhine  daily  removes  from  the  country 
supplying  its  waters  an  amount  of  nitric  acid  equivalent 
to  220  tons  of  saltpeter.  The  Seine  carries  daily  into  the 
Atlantic  270  tons,  and  the  Mle  pours  1,100  tons  into  the 
Mediterranean  every  twenty-four  hours. 

In  the  wells  of  crowded  cities  the  proportion  of  nitrates 
Is  much  higher.  In  the  older  parts  of  Paris  the  well  wa- 
ters contain  as  much  as  one  part  of  niter  (or  its  equiva- 
lent of  other  nitrates)  in  500  of  water. 

The  soil  may  experience  a  loss  of  nitrates  by  the  com- 
plete reduction  of  nitric  acid  to  gaseous  nitrogen,  or  by 
the  formation  of  inert  compounds  with  humus,  as  will  be 
noticed  in  the  next  section. 

Loss  of  assimilable  nitrogen  by  the  washing  of  nitrates 
from  the  soil  may  be  hindered  to  some  extent  in  compact 
soils  by  the  fact  just  noticed  that  nitric  acid  is  liable  to  be 
converted  into  ammonia,  which  is  at  once  rendered  com- 
paratively insoluble. 


THE    NITRIC   ACID    OF    THE    SOIL. 


271 


Nitric  Acid  as.  Food  to  Plants.— Experiments  demon- 
strating that  nitric  acid  is  capable  of  perfectly  supplying 

vegetation  with 
nitrogen  were 
first  made  hy 
Bouss  i  11  g  a  11 1 1 
{Agrono'inie , 
Chimie  Agrl- 
cole^etG.^  1,  210). 
We  give  an  ac- 
count of  some 
of  these. 

Two  seeds  of 
a  dwarf  Sunflow- 
er [Ilelianthiis 
argophyllus), 
were  planted  in 
each  of  three 
pots,  the  soil  of 
which,  consist- 
ing of  a  mixture 
of  brick  -  dust 
and  sand,  as  well 
as  the  pots  them- 
selves, had  been 
thoroughly 
freed  from  all  ni- 
trogenous com- 
pounds by  igni- 
tion and  wash- 
ing with  distill- 
l^ig.  9.  ed    water.      To 

the  soil  of  the  pot  A,  fig.  9,  nothing  was  added  save  the 
two  seeds,  and  distilled  water,  with  which  all  the  j)lants 
were  watered  from  time  to  time.  With  the  soil  of  pot 
C,  were  incorporated  small  quantities  of  phosphate  of  lime, 


272 


HOW    CSOPS    FEED. 


of  ashes  of  clover,  and  bicarbonate  of  potash,  in  order  that 
the  plants  growing  in  it  might  have  an  abundant  supply 
of  all  the  ash-ingredients  they  needed.  Finally,  the  soil 
of  pot  D  received  the  same  mineral  matters  as  pot  C,  and, 
in  addition,  a  small  quantity  (1.4  gram)  of  nitrate  of  pot- 
ash. The  seeds  were  sown  on  the  5th  of  July,  and  on  the 
oOth  of  September,  the  plants  had  the  relative  size  and 
appearance  seen  in  the  figure,  where  they  are  represented 
in  one-eighth  of  the  natural  dimensions. 

For  the  sake  of  comparison,  the  size  of  one  of  the 
largest  leaves  of  the  same  kind  of  Sunflower  that  grew 
in  the  garden  is  represented  at  D,  in  one-eighth  of  its 
natural  dimensions. 

E'othing  can  be  more  striking  than  the  influence  of  the 
nitrate  on  the  growth  of  this  plant,  as  exhibited  in  this 
experiment.  The  plants  A  and  C  are  mere  dwarfs,  al- 
though both  carry  small  and  imperfectly  developed  flow- 
ers. The  plant  T>,  on  the  contrary,  is  scarcely  smaller 
than  the  same  kind  of  plant  growing  under  the  best  con- 
ditions of  garden  culture.  Here  follows  a  Table  of  the 
results  obtained  by  the  examination  of  the  plants. 


IS 
§1 

Acquired  by  the 

plants  in  86  days 

of  vegetation. 

1  Nitro- 
Carbon.  \    gen. 

A — nothing  added  to  the  soil 

3.6 

grm. 
0.285 

cubic 

cent. 

2.45 

grm. 
0.114 

grm. 
0  0023 

C— ashes,  phosphate  of  lime,  and  bi- 
carbonate of  potash,  added  to  the 
soil 

4,6 

0.391 

3.42 

0.156 

0.0027 

D— ashes,  phosphate  of  lime,  and  ni- 
trate of  potash,  added  to  the  soil.. 

MS.  3 

21.111 

182.00 

8.444 

0.1666 

We  gather  from  the  above  data : 

1.  That  without  some  compound  of  nitrogen  in  the  soil 
vegetation  cannot  attain  any  considerable  development, 
notwithstanding  all  requisite  ash-ingredients  are  present 


THE   i^ITEIC   ACID    OF    THE    SOIL. 


273 


in  abundance.  Observe  tbat  in  exps.  A  and  C  the  crop 
attained  but  4  to  5  times  greater  weight  than  the  seed, 
and  gathered  from  the  atmosphere  during  86  days  but  2|- 
milligrams  of  nitrogen.  The  crop,  supplied  with  nitrate 
of  potash,  weighed  200  times  as  much  as  the  seed,  and 
assimilated  66  times  as  much  nitrogen  as  was  acquired  by 
A  and  C  from  external  sources. 

2.  That  nitric  acid  of  itself  may  furnish  all  the  nitrogen 
requisite  to  a  normal  vegetation. 

In  another  series  of  experiments  {Agronomic^  etc.^  I,  pp. 
227-233)  Boussingault  prej^ared  four  pots,  each  containing 
145  grams  (about  5  oz.  avoirdupois)  of  calcined  sand 
with  a  little  phosphate  of  lime  and  ashes  of  stable-dung, 
and  planted  in  each  two  Sunflower  seeds.  To  three  of 
the  pots  he  added  weighed  quantities  of  nitrate  of  soda — 
to  No.  3  twice  as  much  as  to  No.  2,  and  to  No.  4  three 
times  as  much  as  to  No.  3 ;  No.  1  received  no  nitrate. 
The  seeds  germinated  duly,  and  the  plants,  sheltered  from 
rain  and  dew,  but  fully  exposed  to  air,  and  watered  with 
water  exempt  from  ammonia,  grew  for  50  days.  In  the 
subjoined  Table  is  a  summary  of  the  results. 


i 

i 

§. 

b 
^ 

5^0 

III 

Relative  loeights  of 
matter  organized, 
that  of  first  Exp. 
taken  as  unity. 

Relative  lueights  of 
N.  at   disposal  of 
crojjs,  that  of  the 
first  Exp.  taken  as 
unity. 

grms. 

grms. 

grms. 

grms. 

grms. 

grms. 

grms. 

grms. 

1.. 

2.. 
3.. 
4.. 

0.0033 
0.0033 
0.0033 
0.0033 

0.0000 
0.0033 
0.0066 
0.0264 

0.0033 
0.0066 
0.0099 
0.0297 

0.0053 
0.0063 
0.0097 
0.0251 

0.0020t 
0.0002$ 
0.0002; 
0.0046$ 

0.397 
0.720 
1.130 
3.280 

1 

1.8 

2.8 
8.5 

1 
2 
3 
9 

*  N==Nitrogen. 


Ill  the  first  Exp.  a  trifling  quantity  of  nitrogen  was 
gathered  (as  ammonia  ?)  from  the  air.     In  the  others,  and 
especially  in  the  last,  nitrate  of  soda  remained  in  the  soil, 
12* 


274  HOW    CEOPS   FEED. 

not  having  been  absorbed  entirely  by  the  plants.  Observe, 
however,  what  a  remarkable  coincidence  exists  between 
the  ratios  of  supply  of  nitrogen  in  form  of  a  nitrate  and 
those  of  growth  of  the  several  crops,  as  exhibited  in  the 
last  two  columns  of  the  Table.  Nothing  could  demon- 
strate more  strikingly  the  nutritive  function  of  nitric  acid 
than  these  admirable  investigations. 

Of  the  multitude  of  experiments  on  vegetable  nutrition 
which  have  been  recently  made  by  the  process  of  water- 
culture  {H.  C.  G.,  p.  167),  nearly  all  have  depended  upon 
nitric  acid  as  the  exclusive  source  of  nitrogen,  and  it  has 
proved  in  all  cases  not  only  adequate  to  this  purpose,  but 
far  more  certain  in  its  effects  than  ammonia  or  any  other 
nitrogenous  compound. 


§  ^' 

mTKOGENOUS     ORGANIC    MATTERS    OF    THE     SOIL. 

AVAILABLE    NITROGEN.— QUANTITY    OF    NITROGEN 
REQUIRED    FOR    CROPS. 

In  the  minerals  and  rocks  of  the  earth's  surface  nitrogen 
is  a  very  small,  scarcely  appreciable  ingredient.  So  far  as 
we  now  know,  ammonia-salts  and  nitrates  (nitrites)  are 
the  only  mineral  compounds  of  nitrogen  found  in  soils. 
When,  however,  organic  matters  are  altered  to  humus, 
and  become  a  part  of  the  soil,  its  content  of  nitrogen  ac- 
quires significance.  In  peat,  which  is  humus  compara- 
tively free  from  earthy  matters,  the  proportion  of  nitrogen 
is  often  very  considerable.  In  32  specimens  of  peat  ex- 
amined by  the  author  {Feat  and  its  Uses  as  Fertilizer  and 
Fuel.,  p.  90),  the  nitrogen,  calculated  on  the  organic  'mat- 
ters., ranged  from  1.12  to  4.31  per  cent,  the  average  being 
2.6  per  cent.  The  average  amount  of  nitrogen  in  the  air- 
dry  and  in  some  cases  highly  impure  peat,  was  1.4  per 
cent.     This  nitrogen  belongs  to  the  organic  matters  in 


Is^ITEOGENOUS    OKGA^'IC    3IATTERS    OF   THE    SOIL.       275 

great  part,  but  a  small  jDroportion  of  it  being  in  the  form 
of  ammonia-salts  or  nitrates. 

In  1846,  Krocker,  in  Liebig's  laboratory,  first  estimated 
the  nitrogen  in  a  number  of  soils  and  marls  {An7i.  Ch.  u. 
PA.,  58,  387).  Ten  soils,  wbich  were  of  a  clayey  or  loamy 
character,  yielded  from  0.11  to  0.14  per  cent;  three  sands 
gave  from  0.025  to  0.074  per  cent ;  seven  marls  contained 
0.004  to  0.083  per  cent. 

Numerous  examinations  have  since  been  made  by  An- 
derson, Liebig,  Ritthausen,  Wolfi",  and  others,  v^ith  simi- 
lar results. 

In  all  but  his  latest  writings,  Liebig  has  regarded  this 
nitrogen  as  available  to  vegetation,  and  in  fact  designated 
it  as  ammonia.  "Way,  Wolff,  and  others,  have  made  evi- 
dent that  a  large  portion  of  it  exists  in  organic  combina- 
tion. Boussingault  {Agro7iomie,  T.  I)  has  investigated 
the  subject  most  fully,  and  has  shown  that  in  rich  and 
highly  manured  soils  nitrogen  accumulates  in  considerable 
quantity,  but  exists  for  the  most  part  in  an  insoluble  and 
inert  form.  In  the  garden  of  Liebfrauenberg,  which  had 
been  heavily  manured  for  centuries,  but  4°|g  of  the  total 
nitrogen  existed  as  ammonia-salts  and  nitrates.  The  soil 
itself  contained — 

Total  nitrogen,  0.261      per  cent. 
Ammonia,  0.0022       "      " 

Mtricacid,         0.00034     "      " 

The  subjoined  Table  includes  the  results  of  Boussin- 
gault's  examinations  of  a  number  of  soils  from  France  and 
South  America,  in  which  are  given  the  quantities  of  am- 
monia, of  nitric  acid,  expressed  as  nitrate  of  potash,  and 
of  nitrogen  in  organic  combination.  These  quantities  are 
stated  both  in  per  cent  of  the  air-dry  soil,  and  in  lbs.  av. 
per  acre,  taken  to  the  depth  of  17  inches.  In  another 
column  is  also  given  the  ratio  of  nitrogen  to  carbon  in  the 
organic  matters.     {Ajwnomie,  T  II,  pp.  14-21.) 


276 


HOW    CPtOPS    FEED. 


Ammokia,  Niteates,  ^nd  Organic  Nitrogen 

OF  VARIOUS 

Soils 

Ammonia. 

Nitrate  of 
potash. 

1  Nitrogen  in 
\org.  co7nbCn. 

s 

^i 

SoUs. 

lbs. 

lbs. 

lbs 

per 

per 

per 

per 

per 

per 

cent. 

acre 

cent 

acre 

cent. 

acre 

f^li 

03 

'Llebfrauenberg,  light  garcl.  soil 

0.0022 

100 

0.0175* 

875 

0.259 

12970 

1:9.3 

O 

Bischwiller,  light  garden  soil... 

0.0020 

100 

0.1526 

7630 

0.295 

14755 

1:9.7 

1' 

Bechelbronii,  wheat  field  clay. 

0.0009 

45 

0.0015 

75 

0.139 

6985 

1:8.2 

^ 

Argentan,  rich  pasture 

0.0060 

300 

0.0046 

230 

0.513 

25650 

1:8 

''Eio  Madeira,   sugar  field,  clay 

0.0090 

450 

0.0004 

20 

0.143 

7140 

1:6.3 

.s 

Rio  Trombctto, forest  heavy  do. 

0.0030 

183 

0.0001 

5 

0.119 

5955 

1:4.9 

Ilio  Negro,  prairie  v.  fine  sand. 

0.003S 

190 

0.0001 

5: 

0.088 

3440 

1:5.6 

s 

Santarem,  cocoa  plantation.. 

0.0083 

415 

0.0011 

55 

0.649 

32450 

1:11 

<^" 

Saracca,  near  Amazon,  loam... 

0.0042 

210 

none 

0.1S2 

9100 

1:8.2 

^ 

Rio  Cupari,  rich  leaf  mould. . . . 

0.0525 

2875 

" 

0.685 

34250 

1:18.8 

"S 

lies  du  Salut,  French  Guiana... 

O.OOSO 

400 

0.0643    3215 

0.543 

27170 

1:11.7 

o 

^Martinique,  susar  field 

0.0055 

275! 

0.0186      9301 

0.112 

5590 

1:8 

*  The  same  soil  whose  partial  analysis  has  just  been  given,  but  examined  for 
nitrates  at  another  time. 

It  is  seen  that  in  all  cases  the  nitrogen  in  the  forms  of 
ammonia  f  and  nitrates  |  is  much  less  than  that  in  organic 
combination,  and  in  most  cases,  as  in  the  Llebfrauenberg 
garden,  the  disparity  is  very  great. 

Nature  of  tbe  Nitrogenoiis  Organic  Matters.  AisiMes, 
— Hitherto  we  have  followed  Mulder  in  assuming  that  the 
humic,  ulmic,  crenic,  and  apocrenic  acids,  are  destitute  of 
nitrogen.  Certain  it  is,  however,  that  natural  humus  is 
never  destitute  of  nitrogen,  and,  as  we  have  remarked  in 
case  of  peat,  contains  this  element  in  considerable  quanti- 
ty, often  3  per  cent  or  more.  Mulder  teaches  that  the 
acids  of  humus,  themselves  free  from  nitrogen,  are  nat- 
urally combined  to  ammonia,  but  that  this  ammonia  is 
with  difficulty  expelled  from  them,  or  is  indeed  impossible  to 
separate  completely  by  the  action  of  solutions  of  the  fixed 
alkalies.  In  all  chemistry,  beside,  there  is  no  example 
of  such  a  deportment,  and  we  may  well  doubt  whether 
the  ammonia  that  is  slowly  evolved  when  natural  humus 
is  boiled  with  potash  is  thus  expelled  from  a  humate  of 
ammonia.     It  is  more  accordant  with  general  analogies  to 


t  Ammonia  contains  82.4  per  cent  of  nitrogen. 

X  Nitrate  of  potash  contains  13.8  par  cent  of  nitrogen. 


NirEOGENOL^S    OEGANIC    MATTEES    OF   THE    SOIL.       277 

suppose  that  it  is  generated  by  the  action  of  the  alkali. 
In  fact,  there  are  a  large  number  of  bodies  which  manifest 
a  similar  deportment.  Many  substances  which  are  pro- 
duced from  ammonia-compounds  by  heat  and  otherwise, 
and  called  amides^  to  which  allusion  has  been  already 
made,  p.  276,  are  of  this  kind.  Oxalate  of  ammonia,  when 
heated  to  decomposition,  yields  oxamide,  which  contains 
the  elements  of  the  oxalate  minus  the  elements  of  two 
molecules  of  water,  viz.. 

Oxalate  of  ammonia,         Oxamide.  "Water. 

2  (N  HJ  C,  O,  ^  2  (^  HJ  C,  O,  +  2  H,0 

On  boiling  oxamide  with  solution  of  potash,  ammonia 
is  reproduced  by  the  taking  up  of  two  molecules  of  water, 
and  passes  off  as  a  gas,  while  oxalate  of  potash  remains  in 
the  liquid. 

Nearly  every  organic  acid  known  has  one  or  several 
amides,  bearing  to  it  a  relation  similar  to  that  thus  sub- 
sisting between  oxalic  acid  and  oxamide. 

Asparagine,  a  crystallizable  body  found  in  asparagus 
and  many  other  plants,  already  mentioned  as  an  amide,  is 
thought  to  be  an  amide  of  malic  acid. 

Urea,  the  principal  solid  ingredient  of  human  urine,  is 
an  amide  of  carbonic  acid.  Uric  acid,  hippuric  acid,  gua- 
nine, found  also  in  urine;  kreatin  and kreatinine,  occurring 
in  the  juice  of  flesh;  thein,  the  active  principle  of  tea  and 
coffee ;  and  theobromin,  that  of  chocolate,  are  all  regard- 
ed as  amides. 

Amide-like  boaies  are  gelatine  (glue),  the  organic  sub- 
stance of  the  tendons  and  of  bones,  that  of  skin,  hair, 
wool,  and  horn.  The  albuminoids  themselves  are  amide- 
like, in  so  far  that  they  yield  ammonia  on  heating  with 
solutions  of  caustic  alkalies. 

Albuminoids  a  Source  of  tlie  Nitrogen  of  Humus,— 
The  organic  nitrogen  of  humus  may  come  from  the  albu- 
minoids of  the  vegetation  that  has  decayed  upon  or  in  the 


278  HOW    CEOPS    FEED. 

soil.  In  their  alteration  by  decay,  a  portion  of  nitrogen 
assumes  tlie  gaseous  form,  but  a  portion  remains  in  an  in- 
soluble and  comparatively  unalterable  condition,  though 
in  what  particular  compounds  we  are  unable  to  say.  The 
loss  of  carbon  and  hydrogen  from  decaying  organic  mat- 
ters, it  is  believed,  usually  proceeds  more  rapidly  than  the 
waste  of  nitrogen,  so  that  in  humus,  which  is  the  residue 
of  the  change,  the  relative  proportion  of  nitrogen  to  car- 
bon is  greater  than  in  the  original  vegetation. 

Reyers!©!!  of  Nitric  Acid  and  Ammonia  to  inert  Forms. 
— ^It  is  probable  that  the  nitrogen  of  ammonia,  and  of  ni- 
trates, which  are  reducible  to  ammonia  under  certain  con- 
ditions, may  j^ass  into  organic  combination  in  the  soil. 
Knop  (  Versuchs  /St.,  Ill,  228)  found  that  when  peat  or 
soils  containing  humus  were  kept  for  several  months  in 
contact  with  ammonia  in  closed  vessels,  at  the  usual  tem- 
perature of  summer,  the  ammonia,  according  to  its  quan- 
tity, completely  or  in  part  disappeared.  There  having  been 
no  such  amount  of  oxygen  present  as  would  be  necessary  to 
convert  it  into  nitric  acid,  the  only  explanation  is  that  the 
ammonia  combined  with  some  organic  substance  in  the 
humus,  forming  an  amide-like  body,  not  decomposable  by 
the  hypochlorite  of  soda  used  in  Knop's  azometrical  anal- 
ysis. 

Facts  supporting  the  above  view  by  analogy  are  not 
wanting.  When  gelatine  (a  body  of  animal  origin  closely 
related  to  the  albuminoids,  but  containing  18  instead  of 
15"  I Q  of  nitrogen)  is  boiled  with  dilute  acids  for  some 
time,  it  yields,  among  other  products,  sugar,  as  Gerhardt 
has  demonstrated.  Prof  T.  Sterry  Hunt  was  the  first  to 
suggest  {Am.  Jour.  Sci.  S  Arts,  1848,  Yol.  5,  p.  76)  that 
gelatine  has  nearly  the  composition  of  an  amide  of  dextrin 
or  other  body  of  the  cellulose  group,  and  might  be  regard- 
ed as  derived  chemically  from  dextrin  (or  starch)  by  the 
union  of  the  latter  with  ammonia,  water  being  eliminated, 
viz. : 


NITEOGENOFS    OEGAOTiC   MATTERS    OF   THE    SOIL.       279 

Carbohydrate,  Ammonia.     Water.  Gelatine. 

C,,  H„  O..   +   4  NH3  =  6  H,0  +  2  (C.  H„  N,  0,). 

Afterwards  Dusart,  Schtitzenberger,  and  P.  Thenard,  in- 
dependently of  eacli  other,  obtained  by  exposing  dextrin, 
starch,  and  glucose,  to  a  somewhat  elevated  temperature 
(300-360°F.),  in  contact  with  ammonia-water,  substances 
containing  from  11  to  19°  \^  of  nitrogen,  some  soluble  in 
water  and  having  properties  not  unlike  those  of  gelatine, 
others  insoluble.  It  was  observed,  also,  that  analogous 
compounds,  containing  less  nitrogen,  were  formed  at  lower 
temperatures,  as  at  212°  F.  Payen  had  previously  observed 
that  cane  ^gar  underwent  entire  alteration  by  prolonged 
action  of  ammonia  at  common  temperatures. 

These  facts  scarcely  leave  room  to  doubt  that  ammonia, 
as  carbonate,  by  prolonged  contact  with  the  humic  acids 
or  with  cellulose,  and  bodies  of  like  composition,  may 
form  combinations  with  them,  from  which,  by  the  action 
of  alkalies  or  lime,  ammonia  may  be  regenerated. 

It  has  already  been  mentioned  that  when  soils  are  boil- 
ed with  solutions  of  potash,  they  yield  ammonia  continu- 
ously for  a  long  time. 

Boussingault  observed,  as  has  been  previously  remarked, 
that  lime,  when  incorporated  with  the  soil  at  the  ordinary 
temperature,  causes  its  content  of  ammonia  to  increase. 

Soil  from  the  Liebfrauenberg  garden,  mixed  with  ^|^ 
its  weight  of  lime  and  nearly  -J-  its  weight  of  water,  was 
placed  in  a  confined  atmosphere  for  8  months.  On  open- 
ing the  vessel,  a  distinct  odor  of  ammonia  was  perceptible, 
and  the  earth,  which  originally  contained  per  kilogram, 
11  milligrams  of  this  substance,  yielded  by  analysis  303 
mgr.     (See  p.  265,  for  other  similar  results.) 

Alteration  ©f  AlMMinoids  in  ttie  Soil.— Albuminoids 
are  carried  into  the  soil  when  fresh  vegetable  matter  is  in- 
corporated with  it.  They  are  so  susceptible  to  alteration, 
however,  that  under  ordinary  conditions  they  must  speed- 


280  HOW    CEOPS    FEED. 

ily  decompose,  and  cannot  therefore  themselves  be  consid- 
ered as  ingredients  of  the  soil. 

Among  the  proximate  products  of  their  decomposition 
are  organic  acids  (butyric,  valeric,  propionic)  destitute  of 
nitrogen,  and  the  amides  leucin  (Cg  H^g  NO 2)  and  ty rosin 
(Cg  H^j  NOg).  These  latter  bodies,  by  further  decompo- 
sition, yield  ammonia.  As  has  been  remarked,  it  is  proba- 
ble that  the  albuminoids,  when  associated  as  they  are  in 
decay  with  cellulose  and  other  carbohydrates,  may  at 
once  give  rise  to  insoluble  amide-like  bodies,  such  as  those 
whose  existence  in  hiimus  is  evident  from  the  consider- 
ations already  advanced. 

CaM  tSiese  Organic  Bodies  field  Nitrogen  Directly  to 
Plants  ] — Those  nitrogenous  organic  compounds  that  exist 
in  the  soil  associated  with  humus,  which  possess  something 
of  the  nature  of  amides,  though  unknown  to  us  in  a  pure 
state,  appear  to  be  nearly  or  entirely  incapable  of  feeding 
vegetation  directly.  Our  information  on  this  point  is  de- 
rived from  the  researches  of  Boussingault,  whose  papers 
on  this  subject  [De  la  Terre  vegetale  consideree  dans  ses 
effets  sur  la  Yegetatio7i)  are  to  be  found  in  his  Agronomic, 
etc.^  Yols.  I  and  II. 

Boussingault  experimented  with  the  extremely  fertile 
soil  of  his  garden,  which  was  rich  in  all  the  elements 
needful  to  support  vegetation,  as  was  demonstrated  by  the 
results  of  actual  garden  culture.  This  soil  was  especially 
rich  in  nitrogen,  containing  of  this  element  0.26°  ]„,  which, 
were  it  in  the  form  of  ammonia,  would  be  equivalent  to 
more  than  7  tons  per  acre  taken  to  the  depth  of  13  inches ; 
or,  if  existing  as  nitric  acid,  would  correspond  to  more 
than  43  tons  of  saltpeter  to  the  acre  taken  to  the  depth 
just  mentioned. 

This  soil,  however,  when  employed  in  quantities  of  40 
to  130  grams  (1^  to  4:^  oz.  av.)  and  shielded  from  rain 
and  dew,  was  scarcely  more  capable  of  carrying  lui3ins, 
beans,  maize,  or  hemp,  to  any  considerable  development, 


AVAILABLE    IN-ITROGEK    OF    THE    SOIL.  281 

than  the  most  barren  sand.  In  eight  distinct  trials  the 
crops  weighed  (dry)  but  3  to  5  times,  in  one  case  8  times 
(average  4  times),  as  much  as  the  seed;  while  in  sand, 
pumice,  or  burned  soil,  containing  no  nitrogen,  Boussin- 
gault  several  times  realized  a  crop  weighing  6  times  as 
much  as  the  seed,  though  the  average  crop  of  38  experi- 
ments was  but  3  times,  and  the  lowest  result  1|-  times  the 
weight  of  the  seed. 

The  fact  that  the  nitrogen  of  this  garden  soil  was  for 
the  most  part  inert  is  strikingly  shown  on  a  comparison 
of  the  crops  yielded  by  it  to  those  obtained  in  barren 
soil  with  aid  of  known  quantities  of  nitrates. 

In  a  series  of  experiments  with  the  Sunflower,  Boussin- 
gault  {Agronomie^  etc.^  I,  p.  233)  obtained  in  a  soil  desti- 
tute of  nitrogen  a  crop  weighing  (dry)  4.6  times  as  much 
as  the  seeds,  the  latter  furnishing  the  plants  0.0033  grm.  of 
nitrogen.  In  a  second  pot,  with  same  weight  of  seeds,  in 
which  the  nitrogen  was  doubled  by  adding  0.0033  grm.  in 
form  of  nitrate  of  soda,  the  weight  of  crop  was  nearly 
doubled — was  7.6  times  that  of  seeds.  In  a  third  pot  the 
nitrogen  was  trebled  by  adding  0.0066  grm.  in  form  of  ni- 
trate, and  the  crop  was  nearly  trebled  also — was  11.3 
times  the  weight  of  the  seeds. 

In  another  experiment  (p.  271)  the  addition  of  0.194 
grm.  of  nitrogen  as  nitrate  of  potash  to  barren  saud  with 
needful  mineral  matters,  gave  a  crop  weighing  198  times 
as  much  as  the  seeds.  But  in  the  garden  soil,  which  con- 
tained, when  40  grms.  were  employed  0.104  grm.,  and  when 
130  grms.  were  used  0.338  grm.  of  nitrogen,  the  result  of 
growth  was  often  not  greater  than  in  a  soil  that  contained 
no  nitr(5gen,  and  only  in  a  single  instance  surpassed  that 
of  a  soil  to  which  was  added  but  0.0033  grm.  The  fact 
is  thus  demonstrated  that  but  a  very  small  proportion  of 
the  nitrogen  of  this  soil  was  assimilable  to  vegetation. 

From  these  beautiful  investigations  Boussingault  deems 
it  highly  probable  that  in  this  garden  soil,  and  in  soils 


382  HOW    CROPS    FEED. 

generally  which  have  not  been  recently  manured,  ammonia 
and  nitric  acid  are  the  excliisiye  feeders  of  vegetation  with 
nitrogen.  Such  a  view  is  not  indeed  absolutely  demon- 
strated, but  the  experiments  alluded  to  render  it  in  the 
highest  degree  probable,  and  justify  us  in  designating  the 
organic  nitrogen  for  the  most  part  as  inert,  so  far  as  vege- 
table nutrition  is  concerned,  until  altered  to  nitrates  or 
ammonia-salts  by  chemical  change. 

To  comprehend  the  favorable  results  of  garden-culture 
in  such  a  soil,  it  must  be  considered  what  a  large  quantity 
of  earth  is  at  the  disposal  of  the  crop,  viz.,  as  Bousisingault 
ascertained,  57  lbs.  for  each  hill  of  dwarf  beans,  190  lbs. 
for  each  hill  of  potatoes,  470  lbs.  for  each  tobacco  plant, 
and  2,900  lbs.  for  every  three  hop-plants. 

The  quantity  and  condition  of  the  nitrogen  of  Boussin- 
gault's  garden  soil  are  stated  in  the  subjoined  scheme. 

Available  (  Ammonia  0.00220  per  cent  =  Nitrogen  0.00181  per  cent  I  a  nn-io  r^o>.  ^i- 
nitrogen  ]  Nitric  acid  0.00034  "  "  =  "  0.00009  "  "  |- u.uuiy  per  ct. 
Inert  nitrogen— of  organic  compounds .0.2591   "    " 


Total  nitrogen 0.2610  per  ct. 

Calculation  shows  that  in  garden  culture  the  plants 
above  named  would  have  at  their  disposal  in  this  soil  quan- 
tities of  inert  and  available  nitrog-en  as  follows : 


Weight  of  soil 

Inert  nitrogen. 

Available 
nitrogen. 

Bean  (dwarf)  hill 

57  lbs. 

75  grams.* 

1  gram. 

Potato,              " 

190  " 

242 

3  grams. 

Tobacco,  single  plant, 

470  " 

555 

7      " 

Hop,  three  plants. 

2900  " 

S438        " 

41      " 

*      1  gram  =  15  grains  avoirdupois  np.arlJ^ 
17grams=    1  oz.  '•  " 

283      "     =    lib. 

Indirect  Feeding  of  Crops  by  the  Organic  Nitrogen 

of  the  Soil. — In  what  has  been  said  of  the  oxidation  of 
the  organic  matters  of  the  soil,  (whereby  ft  is  probable 
that  their  nitrogen  is  partially  converted  into  nitric  acid,) 
and  of  the  effect  of  alkalies  and  lime  upon  them,  (whereby 
ammonia  is  generated,)  is  given  a  clue  to  the  understand- 


AVAILABLE    NITBOGEIS'    OF    THE    SOIL.  283 

ing  of  their  indirect  nutritive  influence  upon  vegetation. 
By  these  chemical  transformations  the  organic  nitrogen 
may  pass  into  the  two  compounds  which,  in  the  present 
state  of  knowledge,  we  must  regard  as  practically  the  ex- 
clusive feeders  of  the  plant  with  nitrogen.  The  rapidity 
and  completeness  of  the  transformation  depend  upon 
circumstances  or  conditions  which  we  understand  but  im- 
perfectly, and  which  are  extremely  important  subjects  for 
further  investigation. 

©ilSciilty  of  estimatmg"  (lie  AvailaMe  Nitr{>geii  of  any 
Soili — The  vahie  of  a  soil  as  to  its  power  of  supplying 
plants  Avith  nitrogen  is  a  problem  by  no  means  easy  to 
solve.  The  calculations  that  have  just  been  made  from 
the  analytical  data  of  Boussingault  regarding  the  soil  of 
his  garden  are  necessarily  based  on  the  assumption  that 
no  alteration  in  the  condition  of  the  nitrogen  could  take 
place  during  the  period  of  growth.  In  reality,  however, 
there  is  no  constancy  either  in  the  absolute  quantity  of 
nitrogen  in  the  soil  or  in  its  state  of  availability.  Por- 
tions of  nitrogen,  both  from  the  air  and  from  fertilizers, 
may  continually  enter  the  soil  and  assume  temporarily  the 
form  of  insoluble  and  inert  organic  combinations.  Other 
portions,  again,  at  the  same  time  and  as  continually,  may 
escape  from  this  condition  and  be  washed  out  or  gathered 
by  vegetation  in  the  form  of  soluble  nitrates,  as  has  al- 
ready been  set  forth.  It  is  then  manifestly  impossible  to 
learn  more  from  analysis,  than  how  much  nitrogen  is  avail- 
able to  vegetation  at  the  moment  the  sample  is  examined. 
To  estimate  with  accuracy  what  is  assimilable  during  the 
whole  season  of  growth  is  simply  out  of  the  question. 
The  nearest  approach  that  can  be  made  to  this  result  is  to 
ascertain  hov/  much  a  crop  can  gather  from  a  limited  vol- 
ume of  the  soil. 

BretscMeMer's  Experiuieats. — We  may  introduce  here 
a  notice  of  some  recent  researches  made  by  Bretschneider 
in  Silesia,  a  brief  account  of  which  has  appeared  since  the 


284  -  HOW    CROPS    FEED. 

foregoing  paragraphs  Avere  written.  {JahreshericTit  u. 
Ag.  Chem.,  1865,  29.) 

Bret  Schneider's  experiments  were  made  for  the  j^urpose 
of  estimating  how  much  ammonia,  nitric  acid,  and  nitro- 
gen, exist  or  are  formed  in  the  soil,  either  fallow  or  occu- 
pied with  various  crops  during  the  period  of  growth. 
For  this  purpose  he  measured  off  in  the  field  four  plots  of 
ground,  each  one  square  rod  (Prussian)  in  area,  and  sepa- 
rated from  the  others  by  paths  a  yard  wide.  The  soil  of 
one  plot  was  dug  out  to  the  depth  of  12  inches,  sifted, 
and  after  a  board  frame  12  inches  deep  had  been  fitted  to 
the  sides  of  the  excavation,  the  sifted  earth  was  filled  in 
again.  This  and  another — not  sifted — plot  were  planted 
to  sugar  beets,  another  was  sown  to  vetches,  and  the 
fourth  to  oats. 

At  the  end  of  April,  six  accurate  and  concordant  anal- 
yses were  made  of  the  soil.  Afterwards,  at  five  difierent 
periods,  a  cubic  foot  of  soil  was  taken  from  each  plot,  and 
from  the  spaces  between  that  bore  no  vegetation,  for  de- 
termining the  amounts  of  nitric  acid,  ammonia,  and  total 
nitrogen.  The  results  of  this  analytical  Avork  are  given 
in  the  following  Tables,  being  calculated  in  pounds  for  the 
area  of  an  acre,  and  to  the  depth  of  12  inches  (English 
measures*) : 

TABLE    I. 


AMOUNT  OF 

AMMONIA. 

Beet  plot, 
sifted  soil. 

Beet  plot. 

Vetch  plot. 

Oat  plot. 

Vacant  plot. 

End  of  April, 

59 

59 

59 

59 

59 

latli  June, 

15 

48 

41 

32 

28 

30 th  June, 

12 

41 

24 

40 

32 

22d  July, 

9 

29 

39 

22 

29 

13th  August, 

S 

15 

16 

11 

43 

Dth  September, 

0 

16 

16 

r^ 

23 

*  It  is  plain  that  Avlien  the  results  of  analyses  made  on  a  small  amount  of  soil 
are  calculated  upon  the  3,500,000  lbs.  of  soil  (more  or  less)  contained  in  an  acre 
to  the  depth  of  one  foot  (see  p.  158),  the  errors  of  the  analyses,  which  cannot  be 
absolutely  exact,  are  enormously  multiplied.  What  allowance  ought  to  be  made 
in  this  case  we  cannot  say,  but  should  suppose  that  5  per  cent  would  not  be  too 
much.  On  this  basis  differences  of  200-300  lbs.  in  Table  IV  should  be  overlooked. 


AVAILABLE    NITROGEN    OF   THE    SOIL. 


285 


TABLE 

II. 

Amount  of  nitric  acid. 

BeetvloU 
sifted  sou. 

Beet  plot. 

Vetch  plot. 

Oat  plot. 

Vo<^ant  plot. 

End  of  April, 

56 

56 

56 

56 

56 

12th  June, 

281 

270 

102 

28 

106 

SOtli  June, 

328 

442 

15 

93 

318 

22d  July, 

116 

89 

58 

0 

43 

13th  August, 

53 

6 

71 

14 

81 

9th  September, 

0 

•0 
TABLE 

12 

m. 

0 

0 

TOTAIi  ASSIMM-A-RLE  NITROGEN   (OP 

'  AMMONIA  AND  NITRIC   . 

VCID). 

Beetjilot, 
sifted  soil. 

Beet  plot. 

Vetch  plot. 

OatpM. 

Vacant  plot. 

End  of  April, 

63 

63 

63 

63 

63 

12th  June, 

84 

109 

60 

33 

50 

30th  June, 

95 

148 

23 

57     - 

108 

22d  July, 

37 

47 

31 

18 

35 

■13th  August, 

21 

14 

31 

13 

56 

9th  September, 

0 

13 
Tx^BLE 

16 
IV. 

6 

19 

TOTAL  NITROGEN 

OF  THE  SOIL. 

BeetjJlot, 
sifUd  soil. 

Beet  plot. 

Vetch  plot. 

Oat  plot. 

Vacant  plot. 

End  of  April, 

4652 

4652 

4652 

4652 

4652 

12th  June, 

4861 

5209 

5608 

6140 

4720 

SOth  June, 

4667 

5744 

5688 

5514 

4482 

22d  July, 

5398 

5485 

4724 

4924 

13th  August. 

5467 

6316 

6316 

6266 

4412 

9th  September, 

5164 

4656 

6522 

5004 

4294 

From  the  first  Table  we  gather  that  the  quantity  of 
ammonia.,  which  was  considerable  in  the  spring,  dimin- 
ished, especially  in  a  porous  (sifted)  soil  until  September. 
In  the  compact  earth  of  the  uncultivated  path,  its  diminu- 
tion was  less  rapid  and  less  complete.  The  amount  of 
nitric  acid  (nitrates),  on  the  other  hand,  increased,  though 
not  alike  in  any  two  cases.  It  attained  its  maximum  in 
the  hot  weather  of  June,  and  thence  fell  off  until,  at  the 
close  of  the  experiments,  it  was  completely  wanting  save 
in  a  single  instance. 

The  figures  in  the  second  Table  do  not  represent  the 
absolute  quantities  of  nitric  acid  that  existed  in  the  soil 


286  HOW    CROPS    FEED. 

throiigliout  fhe  period  of  experiment,  but  only  those 
amounts  that  remained  at  tlie  time  of  taking  the  samples. 
Wtiat  the  vegetation  took  up  from  the  planted  plots,  what 
was  washed  out  of  the  surface  soil  by  rains,  or  otherwise 
removed  by  chemical  change,  does  not  come  into  the 
reckoning. 

Those  plots,  the  surface  soil  of  which  was  most  occupied 
by  active  roots,  would  naturally  lose  the  most  nitrates  by 
the  agency  of  vegetation ;  hence,  not  imlikely,  the  vetch 
and  oat  plots  contained  so  little  in  June.  The  results  up- 
on the  beet,  and  vacant  ground  plots  demonstrate  that  in 
that  month  a  rapid  foTTnation  of  nitrates  took  place.  It 
is  not,  perhaj^s,  impossible  that  nitrification  also  jDroceeded 
vigorously  in  the  loose  soils  in  July  and  August,  but  was 
not  revealed  by  the  analysis,  either  because  the  vegetation 
took  it  up  or  heavy  rains  washed  it  out  from  the  surface 
soil.  In  the  brief  account  of  these  experiments  at  hand, 
no  information  is  furnished  on  these  points.  Since  moist- 
ure is  essential  to  nitrification,  it  is  possible  that  a  period 
of  dry  weather  coming  on  shortly  before  the  soil  was 
analyzed  in  July,  August,  and  September,  had  an  influence 
on  the  results.  It  is  certainly  remarkable  that  with  the  ex- 
ception of  the  vetch  plot,  the  soil  was  destitute  of  nitrates 
on  the  9th  of  September.  This  plot,  at  that  time,  was 
thickly  covered  with  fallen  leaves. 

We  observe  further  that  the  nature  of  the  crops  influ- 
enced the  accumulation  of  nitrates,  whether  simply  be- 
cause of  the  different  amount  of  absorbent  rootlets  pro- 
duced by  them  and  unequally  developed  at  the  given 
period,  or  for  other  reasons,  we  cannot  decide.''' 

From  the  third  Table  may  be  gathered  some  idea  of  the 
total  quantity  of  nitrogen  that  was  present  in  the  soil  in 


*  It  is  remarkable  that  the  large-leayed  beet  plant  had  a  great  surplus  of  ni- 
trates, while  the  oat  plot  was  comparativelj'-  deficient  in  them.  Has  this  fact  any 
connection  with  what  has  been  stated  (p.  84)  regarding  the  unequal  power  of 
plants  to  provide  themselves  with  nitrogenous  food  ? 


AVAILABLE    NITEOGEN    OF   THE    SOIL.  287 

a  form,  available  to  crops.  Assuming  that  ammonia  and 
nitric  acid  chiefly,  if  not  exclusively,  supply  vegetation 
with  nitrogen,  it  is  seen  that  the  greatest  quantity  of 
available  nitrogen  ascertained  to  be  present  at  any  time  in 
the  soil  was  148  lbs.  per  acre,  taken  to  the  depth  of  one 
foot.  This,  as  regards  nitrogen,  corresponds  to  the  follow- 
ing dressings: — 

lbs.  per  acre. 
Saltpeter  (nitrate  of  potash)  -        -         1068 

Chili  saltpeter  (nitrate  of  soda)  -  898 

Sulphate  of  ammonia      -        -        -        -  909 

Peruvian  guano  (14  per  cent  of  nitrogen)      1057 

The  experience  of  British  farmers,  among  whom  all 
the  substances  above  mentioned  have  been  employed, 
being  that  2  to  3  cwt.  of  any  one  of  them  make  a  large, 
and  5  cwt.  a  very  large,  application  per  acre,  it  is  plain 
that  in  the  surface  soil  of  Bretschneider's  trials  there  was 
formed  during  the  groir^ing  season  a  large  manuring  of 
nitrates  in  addition  to  ichat  was  actually  consumed  hy  the 
crops. 

The  assimilable  nitrogen  increased  in  the  beet  plots  np 
to  the  30th  of  June,  thence  rapidly  diminished  as  it  did 
in  the  soil  of  the  paths.  In  the  oat  and  vetch  plots  the 
soil  contained,  at  none  of  the  times  of  analysis,  so  much 
assimilable  nitrogen  as  at  the  beginning  of  the  experi- 
ments. In  September,  all  the  plots  were  much  poorer  in 
available  nitrogen  than  in  the  spring. 

Table  lY  confirms  what  Bonssingault  has  taught  as  to 
the  vast  stores  of  nitrogen  which  may  exist  in  the  soil. 
The  amount  here  is  more  than  two  tons  per  acre.  We  ob- 
serve further  that  in  none  of  the  cultivated  plots  did  this 
amount  at  any  time  fall  below  this  figure ;  on  the  other 
hand,  in  most  cases  it  was  considerably  increased  during  the 
period  of  experiment.  In  the  uncultivated  plot,  perhaps, 
the  total  nitrogen  fell  off  somewhat.  This  difference  may 
have  been  due  to  the  root  fibrils  that,  in  spite  of  the  ut- 


288 


HOW    CEOPS    TEED. 


most  care,  unavoidably  remain  in  a  soil  from  which  grow- 
ing vegetation  is  removed.  The  regular  and  great  increase 
of  total  nitrogen  in  the  vetch  plot  was  certainly  due  in 
part  to  the  abundance  of  leaves  that  fell  from  the 
plants,  and  covered  the  surface  of  the  soil.  But  this  ni- 
trogen, as  well  as  that  of  the  standing  crops,  must  have 
come  from  the  atmosphere,  since  the  soil  exhibited  no 
diminution  in  its  content  of  this  element. 

We  have  here  confirmation  of  the  view  that  ammonia^ 
as  naturally  supplied^  is  of  very  trifling  importance  to 
vegetation,  and  that,  consequently,  nitrates  are  the  chief 
natural  means  of  providing  nitrogen  for  crops.  The  fact 
that  atmospheric  nitrogen  becomes  a  part  of  the  soil  and 
enters  speedily  into  organic  and  inert  combinations,  also 
aj^pears  to  be  sustained  by  these  researches. 

Quantity  ©f  Nitrogen  needful  for  MaximiiM  ^rain 
CropSi — Hellriegel  has  made  experiments  on  the  eflects 
of  various  quantities  of  nitrogen  (in  the  form  of  nitrates) 
on  the  yield  of  cereals.  The  plants  grew  in  an  artificial 
soil  consisting  of  pure  quartz  sand,  with  an  admixture  of 
ash-ingredients  in  such  proportions  as  trial  had  demon- 
strated to  be  appropriate.  All  the  conditions  of  the  ex- 
periments were  made  as  nearly  alike  as  possible,  except  as 
regards  the  amount  of  nitrogen,  which,  in  a  series  of  eight 
trials,  ranged  from  nothing  to  84  parts  per  1,000,000  of  soil. 

The  subjoined  Table  contains  his  results. 

EFFECTS   OP  VAPJOUS   PROPORTIONS   OP   ASSIMILABLE   NITROGEN 
IN  THE  SOIL. 


Nitrogen  in 

Yield  of  G-raiJi,  in  lbs. 

1,000,000 

lbs.  of  soil. 

Wheat. 

Rye. 

Oats. 

Found 

Calculated 

Found 

Calculated 

Found 

Calculated 

0 

0.002 
Increase 

0.218 
Increase 

0.330 
Increase 

7 

0.553 

0.926 

0.832 

0.936 

0.929 

1.168 

14 

1.708 

1.851 

1.944 

1.933 

2.605 

2.33G 

21 

2.767 

2.777 

2.669 

2.899 

3.845 

3.503 

28 

3.763 

3.703 

4.172 

3.866 

6.211 

4.671 

42 

6.065 

5.554 

5.162 

5.798 

7.030 

7.007 

56 

7.198 

7.406 

7.163 

7.732 

9.052 

9.342 

84 

9.257 

9.257 

8.698 

8.698 

9.342 

9.342 

DECAY  OF  NITROGENOUS  BODIES,  289 

From  numerous  other  experiments,  not  published  at 
this  writing,  Helh-iegel  believes  himself  justified  in  assum- 
ing that  the  highest  yield  thus  observed,  with  84  lbs.  of 
nitrogen  in  1,000,000  of  soil,  might  have  been  got  with 
70  lbs.  of  nitrogen  in  case  of  wheat,  with  63  lbs.  in  case 
of  rye,  and  with  56  lbs.  in  case  of  oats.  On  this  assump- 
tion he  has  calculated  the  yield  of  each  of  these  crops, 
and  the  figures  obtained  (see  Table)  present  on  the  whole 
a  remarkable  coincidence  with  those  directly  observed. 

§  ^' 

DECAY   OF   NITROGENOUS  BODIES. 

We  have  incidentally  noticed  some  of  the  products  of 
the  decay  of  nitrogenous  bodies,  viz.,  those  Avhich  remain 
in  the  soil.  We  may  now,  with  advantage,  review  the 
subject  connectedly,  and  make  our  account  of  this  process 
more  complete. 

It  will  be  needful  in  the  first  place  to  give  some  ex- 
planations concerning  the  nature  of  the  familiar  trans- 
formations to  which  animal  and  vegetable  matters  are 
subject. 

By  the  word  decay,  as  popularly  employed,  is  under- 
stood a  series  of  chemical  changes  which  are  very  differ- 
ent in  their  manifestations  and  results,  according  to  the 
circumstances  under  which  they  take  place  or  the  kinds 
of  matter  they  attack.  Under  one  set  of  conditions  we 
have  slow  decay,  or,  as  Liebig  has  fitly  designated  it, 
eren  ausis  y*  under  others  fermentation ;  and  under  still 
others  putrefaction. 

Eremecausis*  is  a  slow  oxidation,  and  requires  the 
constant  presence  of  an  excess  of  free  oxygen.  It  pro- 
ceeds upon  vegetable  matters  which  are  comparatively 


♦From  the  Greek,  signifying  slow  combustion. 

13 


290  now   CHOPS    FEED. 

difficult  of  alteration,  such  as  stems  and  leaves,  consist- 
ing chiefly  of  cellulose,  with  but  little  albuminoids,  and 
both  in  insoluble  forms. 

What  is  said  in  a  former  paragraph  on  the  "  Decay  of 
Vegetation,"  p.  137,  applies  in  general  to  eremecausis. 

FerMeiltatioil  is  a  term  commonly  applied  to  any 
seemingly  spontaneous  change  taking  place  with  vegeta- 
ble or  animal  matters,  wherein  their  sensible  qualities 
suffer  alteration,  and  heat  becomes  perceptible,  or  gas  is 
rapidly  evolved.  Chemically  speaking,  fermentation  is 
the  breaking  up  of  an  organic  body  by  chemical  decom- 
position, which  may  go  on  in  absence  of  oxygen,  and  is 
excited  by  a  substance  or  an  organism  called  a  ferment. 

There  are  a  variety  of  fermentations,  viz.,  the  vinous,  acetic,  lactic,  etc. 
In  vinous  fermentation,  the  yeast-fungus,  Torvula  cerevisice,  vegetates 
in  an  impure  solution  of  sugar,  and  causes  the  latter  to  hrealc  up  into 
alcohol  and  carbonic  acid  with  small  quantities  of  other  products.  In 
the  acetic  fermentation,  the  vinegar-plant,  Mycoderma  vini,  is  believed 
to  facilitate  the  conversion  of  alcohol  into  acetic  acid,  but  this  change 
is  also  accomplished  by  platinum  sponge,  which  acts  as  a  ferment.  In 
the  lactic  fermentation,  a  fungus,  Fenicilium  glaucurii,  is  thought  to  de- 
termine the  conversion  of  sugar  into  lactic  acid,  as  in  the  souring  of  milk. 

The  transformation  of  starch  into  sugar  has  been  termed  the  saccha- 
rous  fermentation,  diastase  being  the  ferment. 

Putrefactioil}  or  putrid  fermentation,  is  a  rapid  internal 
change  which  proceeds  in  comparative  absence  of  oxygen. 
It  most  readily  attacks  animal  matters  which  are  rich  in 
albuminoids  and  other  nitrogenous  and  sulphurized  prin- 
ciples, as  flesh,  blood,  and  urine,  or  the  highly  nitrogenous 
parts  of  plants,  as  seeds,  when  they  are  fully  saturated 
with  water.  Putrefying  matters  commonly  disengage 
stinking  gases.  According  to  Pasteur  putrefaction  is  oc- 
casioned by  the  growth  of  animalcules  ( Vibrios). 

Fermentation  is  usually  and  putrefaction  is  always  a 
reducing  (deoxidizing)  jDrocess,  for  either  the  ferment  it- 
self or  the  decomposing  substances,  or  some  of  the  prod- 
ucts of  decomposition,  are  highly  prone  to  oxidation,  and 


DECAY    OF   NITROGENOUS    BODIES.  291 

in  absence  of  free  oxygen  may  remove  this  element  from 
reducible  bodies  (Traube,  FermentwirJcungen^  pp.  63-78). 

In  a  mixture  of  cellulose,  sugar,  and  albuminoids,  ere- 
mecausis,  fermentation,  and  putrefaction,  may  all  proceed 
simultaneously. 

When  the  albuminoids  decay  in  the  soil  associated  with 
carbohydrates  and  humus,  the  final  results  of  their  altera- 
tion may  be  summed  up  as  follows  : 

1.  Carbon  unites  mainly  with  oxygen,  forming  carbonic 
acid  gas,  which  escapes  into  the  atmosphere.  With  im- 
perfect supplies  of  oxygen,  as  Avhen  submerged  in  water, 
carbonic  oxide  (CO)  and  marsh  gas  (CHJ  are  formed.  A 
portion  of  carbon  remains  as  humus. 

2.  Hydrogen^  for  the  most  part,  combines  with  oxygen, 
yielding  water.  In  deficiency  of  oxygen,  some  hydrogen 
escapes  as  a  carbon  compound  (marsb-gas),  or  in  the  free 
state.  If  humus  remains,  hydrogen  is  one  of  its  con- 
stituents. 

3.  a.  Nitrogen  always  unites  to  a  large  extent  with 
hydrogen,  giving  ammonia,  which  escapes  as  gaseous  car- 
bonate in  considerable  quantity,  unless  from  presence  of 
carbohydrates  much  humus  is  formed,  in  which  case  it 
may  be  nearly  or  entirely  retained  by  the  latter.  Lawes, 
Gilbert,  and  Pugh,  {Phil.  Trans.  1861,  IL,  p.  501)  made 
observations  on  the  decay  of  wheat,  barley,  and  bean 
seeds,  either  entire  or  in  form  of  meal,  mixed  with  a  large 
quantity  of  soil  or  powdered  pumice,  and  exposed  in  vari- 
ous conditions  of  moisture  to  a  current  of  air  for  six 
months.  They  found  in  nine  experiments  that  from  11  to 
58°  |g  of  the  nitrogen  was  converted  into  ammonia,  al- 
tliough  but  a  trifling  proportion  of  this  (on  the  average 
but  0.4°|  J  escaped  in  the  gaseous  form. 

h.  In  presence  of  excess  of  oxygen,  a  portion  of  nitro- 
gen usually  escapes  in  the  free  state.  Reiset  proved  the 
escape  of  free  nitrogen  from  fermenting  dung.     Boussin- 


292  HOAY    CEOPS    FEED. 

gault,  in  his  investigations  on  the  assimilability  of  free 
nitrogen,  found  in  yarious  vegetation-experiments,  in 
which  crushed  seeds  were  used  as  fertilizers,  that  nitrogen 
was  lost  by  assuming  some  gaseoMS  form.  This  loss  prob- 
ably took  place  to  some  slight  extent  as  ammonia,  but 
chiefly  as  free  nitrogen.  Lawes,  Gilbert,  and  Pugh,  found 
in  thirteen  out  of  fifteen  trials,  including  the  experiments 
just  referred  to,  that  a  loss  of  free  nitrogen  took  place, 
ranging  from  2  to  40  per  cent  of  the  total  quantity  con- 
tained originally  in  the  vegetable  matters  submitted  to 
decomposition.  In  six  exj^eriraents  the  loss  was  12  to  13 
per  cent.  In  the  two  cases  where  no  loss  of  nitrogen  oc- 
curred, nothing  in  the  circumstances  of  decay  was  discov- 
erable to  which  such  exceptional  results  could  be  at- 
tributed. Other  experiments  (JPhil  Trans.  1861,  II.,  p. 
509)  demonstrated  that  in  absence  of  oxygen  no  nitrogen 
was  evolved  in  the  free  state. 

c.  Nitric  acid  is  not  formed  from  the  nitrogen  of  or- 
ganic bodies  in  rapid  or  ^putrefactive  decay,  but  only  in 
slow  oxidation  or  eremecausis  of  humified  matters. 
Pelouze  found  no  nitrates  in  the  liquor  of  dung  heaps. 
Lawes,  Gilbert,  and  Pugh,  {loc.  c^'^.)*  found  no  nitric  acid 
when  the  seed-grains  decayed  in  ordinary  air,  nor  was  it 
produced  when  ozonized  air  was  passed  over  moist  bean- 
meal,  either  alone  or  mixed  with  burned  soil  or  with 
slaked  lime,  the  experiments  lasting  several  months.  It 
thus  appears  that  the  carbon  and  hydrogen  of  organic 
matters  have  such  an  affinity  for  oxygen  as  to  prevent  the 
nitrogen  from  acquiring  it  in  the  quicker  stages  of  decay. 
More  than  this,  as  Pelouze  has  shown  ( Comptes  Rendus, 
XLiy.,  p.  118),  putrefying  matters  rob  nitric  acid  of  its 
oxygen  and  couA^ert  it  into  ammonia.  We  have  already 
remarked  that  putrefaction  and  fermentation  are  reducing 
processes,  and  until  they  have  run  their  course  and  the 
organic  matters  have  passed  into  the  comparatively  stable 
forms  of  humus,  their  nitrogen  appears  to  be  incapable  of 


THE    NITEOGEIS'OUS    PRINCIPLES    OF    UEINE.  293 

oxidation.  So  soon  as  compounds  of  carbon  and  hydrogen 
are  formed,  which  unite  but  slowly  with  free  oxygen,  so 
that  the  latter  easily  maintains  itself  in  excess,  then  and 
not  before,  the  nitrogen  begins  to  combine  with  oxygen. 
4.  Finally,  the  sulphur  of  the  albuminoids  may  be  at 
first  partially  dissipated  as  sulphuretted  hydrogen  gas, 
while  in  the  slower  stages  of  decay,  it  is  oxidized  to  sul- 
phuric acid,  which  remains  as  sulphates  in  the  soil. 

§8. 

THE  NITROGENOUS  PRINCIPLES  OF  URINE. 

The  question  "  How  Crops  Feed  "  is  not  fully  answered 
as  regards  the  element  Nitrogen,  without  a  consideration 
of  certain  substances — ingredients  of  urine — which  may 
become  incorporated  with  the  soil  in  the  use  of  animal 
manures. 

Professor  Way,  in  his  investigation  on  the  "  Power  of 
Soils  to  Absorb  Manure,"  describes  the  following  remark- 
able experiment :  "  Three  quantities  of  fresh  urine,  of 
2,000  grains  each,  were  measured  out  into  similar  glasses. 
With  one  portion  its  own  weight  of  sand  was  mixed  ; 
with  another,  its  own  weight  of  white  clay ;  the  third 
being  left  without  admixture  of  any  kind.  When  smelt 
immediately  after  mixture,  the  sand  appeared  to  have 
had  no  effect,  whilst  the  clay  mixture  had  entirely  lost 
thfe  smell  of  urine.  The  three  glasses  were  covered  light- 
ly with  paper  and  put  in  a  warm  place,  being  examined 
from  time  to  time.  In  a  few  hours  it  was  found  that  the 
urine  containing  sand  had  become  slightly  j^utrid ;  then 
followed  the  natural  urine ;  but  the  quantity  with  which 
clay  had  been  mixed  did  not  become  putrid  at  cdl^  and 
at  the  end  of  seven  or  eight  weeks  it  had  only  the  pecu- 
liar smell  of  fresh  urine,  without  the  slightest  putridity. 
The  surface  of  the  clay,  however,  became  afterwards  cov- 


294  HOW    CEOPS   FEED. 

ered  with  a  luxuriant  growth  of  confervse,  which  did  not 
happen  in  the  other  glasses."  {Jour.  Hoy.  Ag.  Soc.  of 
Eng.,  XL,  366.) 

Professor  Way  likewise  found  that  filteriug  urine 
through  clay  or  simply  shaking  the  two  together,  allow- 
ing the  liquid  to  clear  itself,  and  j)Ouring  it  off,  sufficed  to 
prevent  putrefaction,  and  keep  the  urine  as  if  fresh  for  a 
month  or  more.  Cloez  found,  as  stated  on  p.  264,  that  in 
a  mixture  of  moistened  pumice-stone,  carbonate  of  lime, 
and  urea  (the  nitrogenous  principle  of  urine),  no  nitrates 
were  formed  during  eight  months'  exposure  to  a  slow 
current  of  air. 

These  facts  make  it  necessary  to  consider  in  what  state 
the  nitrogen  of  urine  is  absorbed  and  assimilated  by 
vegetation. 

Urine  contains  a  number  of  compounds  rich  in  nitro- 
gen, being  derived  from  the  waste  of  the  food  and  tissues 
of  the  animal,  which  require  a  brief  notice. 

Urea  (CO  K^HJ*  may  be  obtained  from  the  urine  of 
man  as  a  white  crystalline  mass  or  in  distinct  transparent 
rhombic  crystals,  which  remain  indefinitely  unaltered  in 
dry  air,  and  have  a  cooling,  bitterish  taste  like  saltpeter. 
It  is  a  weak  base,  and  chemists  have  prepared  its  nitrate, 
oxalate,  phosphate,  etc. 

Urea  constitutes  2  to  3  per  cent  of  healthy  human 
urine,  and  a  full-grown  and  robust  man  excretes  of  it 
about  40  grams,  or  l^lg  oz.  av.  daily. 

When  urine  is  left  to  itself,  it  shortly  emits  a  jDutrid 
odor ;  after  a  few  days  or  hours  the  urea  it  contained  en- 
tirely disappears,  and  the  liquid  smells  powerfully  of  am- 
monia.    Urea,  v/hen  in  contact  with  the  animal  matters 


*  Carbon 20.00 

Hydrogen 6.67 

Nitrogen 46.67 

Oxygen 26.66 

100.00 


THE    NITPtOGElSrOUS    PP.IXCIPLES    OF    UPINE.  295 

of  urine,  suffers  decomposition,  and  its  elements,  combin- 
ing with  the  elements  of  water,  are  completely  transformed 
into  carbonate  of  ammonia. 

Urea.  Water.     Carbonate  of  Ammonia. 

CO  ]^,H^  +   2H„0   =  2(]STH3),  H^O,CO,. 

As  we  have  learned  from  Way's  experiments,  clay  is 
able  to  remove  from  urine  the  '' ferment "  which  occasions 
its  putrefaction. 

Urea  is  abundant  in  the  urine  of  all  carnivorous  and 
herbivorous  mammals,  and  exists  in  small  quantity  in  the 
urine  of  carnivorous  birds,  but  has  not  been  detected  in 
that  of  herbivorous  birds. 

Uric  acid  (C^H^N'^Og)'^  is  always  present  in  healthy 
human  urine,  but  in  very  minute  quantity.  It  is  the  chief 
solid  ingredient  of  the  urine  of  birds  and  reptiles.  Here 
it  exists  mainly  as  urate  of  ammonia.**  The  urine  of 
birds  and  serpents  is  expelled  from  the  intestine  as  a  white, 
thicMsh  liquid,  which  dries  to  a  chalk-like  mass.  From 
this,  uric  acid  may  be  obtained  in  the  form  of  a  white 
powder,  which,  when  magnified,  is  seen  to  consist  of  mi- 
nute crystals.  By  powerful  oxidizing  agents  uric  acid  is 
converted  into  oxalate  and  carbonate  of  ammonia,  and 
urea.  Peruvian  guano,  when  of  good  quality,  contains 
some  10  per  cent  of  urate  of  ammonia. 

HippMI'ic  acid  (CgHglSTOJf  is  commonly  abundant  in 
the  urine  of  the  ox,  horse,  and  other  herbivorous  animals. 
By  boiling  down  fresh  urine  of  the  pastured  or  hay-fed 
cow  to  ^  |g  its  bulk,  and  adding  hydrochloric  acid,  hippuric 
acid  crystallizes  out  on  cooling  in  four-sided  prisms,  of- 
ten two  or  three  inches  in  len2;th. 


*  Carbon 35.72        **  Carbon 32.43       t  Carbon 60.74 

Hydrogen 2.38  Hydrogen 3.78  Hydrogen 4.96 

Nitrogen 33.33  Nitrogen 37.84  Nitrogen 7.82 

Oxygen 28.57  Oxygen 25.95  Oxygen 26.48 

100.00  100.00  100.00 


296  HOW    CEOPS    FEED. 

GlySDCOlI  or  l^iycilie'''  is  a  sweet  substance  that  re- 
sults from  the  decomposition  of  hippuric  acid  under  the 
influence  of  various  agents.  It  is  also  a  product  of  the 
action  of  acids  on  gelatine  and  horn. 

Guanine  (C^H^N^O)  f  occurs  to  the  extent  of  about 
^  I2  per  cent  in  Peruvian  guano,  and  is  an  ingredient  of 
the  liver  and  pancreas  of  animals,  whence  it  passes  into 
the  excrement  in  case  of  birds  and  spiders.  By  oxidation 
it  yields  among  other  products  urea  and  oxalic  acid. 

Kreatin  (C^HgKgOJ  I  is  an  organic  base  existing  in 
very  minute  quantity  in  the  flesh  of  animals,  and  occa- 
sionally found  in  urine. 

Cameron  was  the  first,  in  1857,  to  investigate  the  assimi- 
lability  of  urinary  products  by  vegetation.  His  experi- 
ments {Chemistry/  of  Agriculture,  pp.  139-144)  were 
made  with  barley,  which  was  sown  in  an  artificial  soil, 
destitute  of  nitrogen.  Of  four  pots  one  remained  without 
a  supply  of  nitrogen,  another  was  manured  with  sulphate 
of  ammonia,  and  two  received  a  solution  of  urea.  The 
pot  without  nitrogen  gave  plants  8  inches  high,  but  these 
developed  no  seeds.  The  pot  with  sulphate  of  ammonia 
gave  plants  22  inches  high,  and  300  seeds.  Those  with 
urea  gave  respectively  stalks  of  26  and  29  inches  height, 
and  252  and  270  seeds.  The  soil  in  neither  case  contained 
ammonia,  the  usual  decomposition-product  of  urea.  Dr. 
Cameron  justly  concluded  that  urea  enters  plants  un- 
changed, is  assimilated  by  them,  and  equals  ammonia-salts 
as  a  means  of  supplying  nitrogen  to  vegetation. 

The  next  studies  in  this  direction  were  made  by  the  au- 
thor in  1861  {Am.  Jour.  Scieiice,  XLI.,  27).  Experiments 
were  conducted  with  uric  acid,  hippuric  acid,  and  guanine. 


*  Carbon 39.73    +  Carbon 32.00    X  Carbon. . ,- 36.64 

Hydrogen 3.31       Hydrogen 6.6T       Hydrogen 6.S7 

Nitrogen 46.36       Nitrogen 18.67        Nitrogen 32.06 

Osygen 10.60       Oxygen 42.66        Oxygen 24.43 

100.00  100.00  100.00 


THE    NITROGENOUS    PEINCIPLES    OF    URINE.  297 

Washed  and  ignited  flower-pots  were  employed,  to  con- 
tain, for  each  trial,  a  soil  consisting  of  700  grms.  of 
ignited  and  washed  granitic  sand,  mixed  with  0.25  grm. 
sulphate  of  lime,  2  grms.  ashes  of  hay,  prepared  in  a  muffle, 
and  2.75  grms.  bone-ashes.  This  soil  w^as  placed  upon 
100  grms.  of  clean  gravel  to  serve  as  drainage. 

In  each  of  four  pots  containing  the  above  soil  was  de- 
posited, July  6th,  a  weighed  kernel  of  maize.  The  pot?i 
were  watered  with  equal  quantities  of  distilled  water  con- 
taining a  scarcely  appreciable  trace  of  ammonia.  The 
seeds  germinated  in  a  healthy  manner,  the  plants  devel- 
oped slowly  and  alike  until  July  28th,  when  the  addition 
of  nitrogenous  matters  was  begun. 

To  l^o.  1,  no  solid  addition  was  made. 

To  ISTo.  2  was  added,  July  28th,  0.420  grm.  uric  acid. 

To  "No.  3  was  added  1.790  grm.  hippuric  acid,  at  four 
different  times,  viz:  July  28,0.358  grm.,  Aug.  26th,  0.358 
grm.,  Sept.  16th,  0.716  grm.,  Oct.  3d,  0.358  grm. 

To  No.  4  was  added  0.4110  grm.  hydrochlorate  of  gua- 
nine, viz:  July  28th,  0.0822  grm.,  Aug.  26th,  0.0822 
grm.,  Sept.  16th,  0.1644  grm.,  Oct.  3d,  0.0822  grm. 

The  nitrogenous  additions  contained  in  each  case,  0.140 
grm.  of  nitrogen,  and  were  strewn,  as  fine  powder,  over 
the  surface  of  the  soil. 

The  plants  continued  to  grow  or  to  remain  healthy  (the 
lower  leaves  withering  more  or  less)  until  they  were  re- 
moved from  the  soil,  oSTov.  8th. 

The  plants  exhibited  striking  differences  in  their  devel- 
opment. ~No.  1  (no  added  nitrogen)  produced  in  all  seven 
slender  leaves,  and  attained  a  height  of  7  inches.  At  the 
close  of  the  experiment,  only  the  two  newest  leaves  were 
perfectly  fresh  ;  the  next  was  w^ithered  and  dead  through- 
out one-third  of  its  length.  The  newer  portions  of  this 
plant  grew  chiefly  at  the  expense  of  the  older  parts.  ISTo 
sign  of  floral  organs  appeared. 


298~  HO"W   CROPS   PEED. 

'No.  2,  fed  with  uric  acid,  was  the  best  developed  plant 
of  the  series.  At  the  conclusion  of  the  experiment,  it 
bore  ten  vigorous  leaves,  six  of  which  were  fresh,  and  two 
but  partly  withered.  It  vv^as  14  inches  high,  and  carried 
two  iTidimentary  ears  (pistillate  flowers),  from  the  upper 
one  of  which  hung  tassels  6  inches  long. 

ISTo.  3,  supplied  with'  hippuric  acid,  bore  eight  leaves, 
four  of  which  were  withered,  and  two  rudimentary  ears, 
one  of  which  tasseled.     Hei2:ht,  12  inches. 

No.  4,  with  hydrochlorate  of  guanine,  had  six  leaves, 
one  withered,  and  two  ears,  one  of  which  was  tasseled. 
Height,  12  inches.  The  weight  of  the  crops  (dried  at 
212°  F.),  exclusive  of  the  fine  rootlets  that  could  not  be 
removed  from  the  soil,  was  ascertained,  with  the  subjoined 
results. 

12  3  4 

"Without  Hippuric 

Nitrogen.      Uric  Acid.        Acid.  Guanine. 

V/eight  of  dried  crop,   0.1925  grm.    1.9470  grm.    1.0149  grm.    0.9820  grm. 
seed,  0.1644    "         .1725^"       0.1752^"       0.1698     " 


gain,  0.0391     "       1.7745     "      0.8397     "       0.8122     " 

We  thus  have  proof  that  all  the  substances  employed 
contributed  nitrogen  to  the  growing  plant.  This  is  con- 
clusively shown  by  the  fact  that  the  development  of  pis- 
tillate organs,  which  are  especially  rich  in  nitrogen, 
occurred  in  the  three  plants  fed  with  nitrogenous  com- 
pounds, but  was  totally  wanting  in  the  other.  The  rela- 
tion of  matter,  new-organized  by  growth,  to  tliat  derived 
from  the  seed,  is  strikingly  seen  from  a  comparison  of  the 
ratios  of  the  weight  of  the  seed  to  the  increase  of  organ- 
ized matter,  the  former  being  taken  as  unity. 

The  ratio  is  approximatively 

for  No. 


cc 


1, 

1 

0.2 

2, 

1 

10.2 

3, 

1     . 

4.8 

4, 

1 

4.8 

for  No.  1, 

— 

"      "    2, 

— 

"      "    3, 

— 

THE    NITROGENOUS    PRINCIPLES    OF    TJEINE.  299 

The  relative  gain  by  growth,  that  o^  ISTo.  1   assumed  as 

1 
61 
29 

''      "    4,     —  28 

The  crops  were  small,  principally  because  the  supply 
ofunitrogen  was  very  limited. 

These  experiments  demonstrate  that  the  substances 
added,  in  every  case,  aided  growth  by  supplying  nitro- 
gen. They  do  not,  indeed,  prove  that  the  organic  fertil- 
izers entered  as  such  into  the  crop  without  decomposition, 
but  if  urea  escapes  decomposition  in  a  soil,  as  Cameron 
and  Cloez  have  shown  is  true,  it  is  not  to  be  anticipated 
that  the  bodies  employed  in  these  trials  should  suffer  al- 
teration to  ammonia-salts  or  nitrates. 

Hampe  afterwards  experimented  with  urea  and  uric 
acid  by  the  method  of  Water-Culture  (  Vs.  jSt.,  YII.,  308 ; 
VIII.,  225  ;  IX.,  49 ;  and  X.,  175).  He  succeeded  in  pro- 
ducing, by  help  of  urea,  maize  plants  as  large  as  those 
growing  in  garden  soil,  and  fully  confirmed  Cameron's 
conclusion  regarding  the  assimilability  of  this  substance. 
Hampe  demonstrated  that  urea  entered  as  such  into  the 
plant.  In  fact,  he  separated  it,  in  the  pure  state,  from 
the  stems  and  leaves  of  the'maize  which  had  been  pro- 
duced with  its  aid. 

Hampe's  experiments  with  uric  acid  in  solution  showed 
that  this  body  supplied  nitrogen  without  first  assuming 
the  form  of  ammonia-salts,  but  it  suffered  partially  if  not 
entirely  a  decomposition,  the  nature  of  which  was  not 
determined.  Uric  acid  itself  could  not  be  found  in  the 
crop. 

Hampe's  results  with  hippuric  acid  were  to  the  effect 
that  this  substance  furnishes  nitrogen  without  reversion 
to  ammonia,  but  is  resolved  into  other  bodies,  probably 
benzoic  acid  and  glycocoll,  which  are  formed  when  hip- 


300  HOW    CEOPS    FEED. 

pnric  acid  is  subjected  to  the  action  of  strong  acids  or 
ferments. 

Hampe,  therefore,  experimented  with  glycocoll,  and 
from  his  trials  formed  the  opinion  that  this  body  is  di- 
rectly nutritive.  In  fact,  he  obtained  with  it  a  crop  equal 
to  that  yielded  by  ammonia-salts. 

Knop,  who  made,  in  1857,  an  unsuccessful  experiment 
with  hippuric  acid,  found,  in  1866,  that  glycocoll  is  as- 
similated {Chem.  Centralhlatt^  1866,  p.  774). 

In  1868,  Wagner  experimented  anew  with  hippuric 
acid  and  glycocoll.  His  results  confirm  those  of  Hampe. 
Wagner,  however,  deems  it  probable  that  hippuric  acid 
enters  the  plant  as  such,  and  is  decomposed  within  it  into 
benzoic  acid  and  glycocoll  ( T^-.  gt^^  XI.,  p.  294). 

Wagner  found,  also,  that  kreatin  is  assimilated  by 
vegetation. 

The  grand  result  of  these  researches  is,  that  the  nitrog- 
enous (amide-like)  acids  and  bases  which  are  thrown  off 
in  the  urinary  excretions  of  animals  need  not  revert,  by 
decay  or  putrefaction,  to  inorganic  bodies  (ammonia  or 
nitric  acid),  in  order  to  nourish  vegetation,  but  are  either 
immediately,  or  after  undergoing  a  slight  and  easy  altera- 
tion, taken  up  and  assimilated  by  growing  plants. 

As  a  practical  result,  these  facts  show  that  it  is  not 
necessary  that  urine  should  be  fermented  before  using  it 
as  a  fertilizer. 


COMPARATIVE  NUTRITIVE  VALUE  OF  AMMONIA-SALTS  AND 
NITRATES. 

The  evidence  that  both  ammonia  and  nitric  acid  are  ca- 
pable of  supjjlying  nitrogen  to  plants  has  been  set  forth. 
It  has  been  shown  further  that  nitric  acid  alone  can  per- 
fectly satisfy  the  wants  of  vegetation  as  regards  the  ele- 
In  respect  to  ammonia,  the  case  has  not 


YALXJE    OF    AMMONIA    AND    NITEIC    ACID. 


301 


been  similarly  made  out. 
occurs,  naturally,  in  too 


We  have  learned  that  ammonia 
small  proportion,  either  in  the 
atmosphere  or  the  soil,  to  supply  much  nitrogen  to  crops. 
In  exceptioDal  cases,  however,  as  in  the  leaf-mold  of  Rio 
Cupari,  examined  by  Boussingault,  p.  276,  as  well  as  in 
lands  manured  with  fermenting  dung,  or  with  sulphate  or 
muriate  of  ammonia,  this  substance  acquires  importance 
from  its  quantity. 

On  the  assumption  that  it  is  the  nitrogen  of  these  sub- 
stances, and  not  their  hydrogen  or  oxygen,  which  is  of 
value  to  the  plant,  we  should  anticipate  that  17  parts  of 
ammonia  would  equal  54  parts  of  nitric  acid  in  nutritive 
effect,  since  each  of  these  quantities  represents  the  same 
amount  (14  parts)  of  nitrogen.  The  ease  with  which 
ammonia  and  nitric  acid  are  mutually  transformed  favors 
this  view,  but  the  facts  of  experience  in  the  actual  feed- 
ing of  vegetation  do  not,  as  yet,  admit  of  its  acceptance. 

In  earlier  vegetation-exjjeriments,  wherein  the  nitro- 
genous part  of  an  artificial  soil  (without  humus  or  clay) 
consisted  of  ammonia-salts,  it  was  found  that  these  were 
decidedly  inferior  to  nitrates  in  their  producing  power. 
This  was  observed  by  Yille  in  trials  made  with  wheat 
planted  in  calcined  sand,  to  which  was  added  a  given 
quantity  of  nitrogen  in  the  several  forms  of  nitrate  of 
potash,  sal-ammoniac  (chloride  of  ammonium),  nitrate  of 
ammonia,  and  phosphate  of  ammonia. 

Ville's  results  are  detailed  in  the  following  table.  The 
quantity  of  nitrogen  added  was  0.110  grm.  in  each  case. 


Source  of  Nitrogen. 


straw  and 
Boots. 


Nitrate  of  Potasli. 


Sal-ammoniac ]  tt' 


Nitrate  of  ammonia. 


Phosphate  of  ammonia j  jj 


20.70 
19.22 
15.10 
17.31 
12.20 
14.87 
12.96 
15.82 


Grain. 


Average 
crop. 


6.20  [       o«7i 

7.30  r---^-'^ 


4.93 
3.54 


.18.83 
.?:86[--18.32 
Ul]... IS  AO 


Nitrogen 

in  average 

crop. 


0.221 
0.142 
0.133 
0.133 


303  HOW  cr.ops  feed. 

It  is  seen  that  the  ammonia-salts  gave  about  one-fourth 
less  crop  than  the  nitrate  of  potash.  The  potash  doubt- 
less contributed  somewhat  to  this  difference. 

The  author  began  some  experiments  on  this  jjoint  in 
1861,  which  turned  out  unsatisfactorily  on  account  of  the 
want  of  light  in  the  apartment.  In  a  number  of  these, 
buckwheat,  sown  in  a  weathered  feldspatbic  sand,  was  ma- 
nured with  equal  quantities  of  nitrogen,  potash,  lime, 
phosphoric  acid,  sulphuric  acid,  and  chlorine,  the  nitrogen 
being  presented  in  one  instance  in  form  of  nitrate  of  potash, 
in  the  others  as  an  ammonia-salt — sulphate,  muriate,  phos- 
phate, or  oxalate. 

Although  the  plants  failed  to  mature,  from  the  cause 
above  mentioned,  the  experiments  plainly  indicated  the 
inferiority  of  ammonia  as  compared  with  nitric  acid. 

Explanations  of  this  fact  are  not  difficult  to  suggest. 
The  most  reasonable  one  is,  perhaps,  to  be  found  in  the 
circumstance  that  clayey  matters  (which  existed  in  the 
soil  imder  consideration)  "  fix  "  ammonia,  i,  e.,  convert  it 
into  a  comparatively  insoluble  compound,  so  that  the 
plant  may  not  be  able  to  appropriate  it  all. 

On  the  other  hand,  Helhiegel  [Aom.  d.  Landio.^  YIL, 
53,  %i.  VIIL,  119)  got  a  better  yield  of  clover  in  artificial 
soil  with  sulphate  of  ammonia  and  phosphate  of  ammonia 
than  with  nitrate  of  ammonia  or  nitrate  of  soda,  the  quan- 
tity of  nitrogen  being  in  all  cases  the  same. 

As  Sachs  and  Knop  developed  the  method  of  Water- 
Culture,  it  was  found  by  the  latter  that  ammonia-salts  did 
not  effectively  replace  nitrates.  The  same  conclusion  was 
arrived  at  by  Stohmann,  in  1861  and  1863  {Senneberg'Q 
Journ.^  1862,  1,  and  1864,  65),  and  by  Rautenberg  and 
Ktihn,  in  1863  {IlennebeTg' s  «7bt<^r;z.,  1864,  107),  who  ex- 
perimented with  sal-ammoniac,  as  well  as  by  Birner  and 
Lucanus,  in  1864  {Ys.  jSt.,  YIIL,  152),  who  employed 
sulphate  and  phosj)hate  of  ammonia. 

The  cause  of  fliilure  lay  doubtless  in  the  fact,  first  noti'^^'^ 


VALUE    OF    AMMONIA   AND    NITEIC    ACID.  303 

by  Ktihn,  that  so  soon  as  ammonia  was  taken  up  by  the 
plant,  the  acid  with  which  it  was  combined,  becoming  free, 
acted  as  a  poison. 

In  1866,  Hampe  {Vs.  jSt.^lX.,  165),  using  phosphate 
of  ammonia  as  the  single  source  of  nitrogen,  and  taking 
care  to  keep  the  solution  but  faintly  acid,  obtained  a 
maize-plant  which  had  a  dry  weight  of  18  grams,  includ- 
ing 36  perfect  seeds ;  no  nitrates  were  formed  in  the 
solution. 

The  same  summer  Ktihn  {Vs.  /St.,  IX.,  167)  produced 
two  small  maize-plants,  one  with  phosphate,  the  other 
with  sulphate  of  ammonia  as  the  source  of  nitrogen,  but 
his  experiments  were  interrupted  by  excessive  heat  in  the 
glass-house. 

In  1866,  Beyer  {Vs.  jSt,  IX.,  480)  also  made  trials  on 
the  growth  of  the  oat-plant  in  a  solution  containing  bi- 
carbonate of  ammonia.  The  plants  vegetated,  though 
poorly,  and  several  blossomed  and  even  produced  a  few 
seeds.  Quite  at  the  close  of  the  experiments  the  plants 
suddenly  began  to  grow,  with  formation  of  new  shoots. 
Examination  of  the  liquid  showed  that  the  ammonia  had 
been  almost  completely  converted  into  nitric  acid,  and  the 
increased  growth  was  obviously  connected  with  this  nitrifi- 
cation. 

In  1867,  Hampe  (  Vs.  jSt.,  X.,  176)  made  new  experi- 
ments with  ammonia-salts,  and  obtained  one  maize-plant 
2^1 2  ft.  high,  bearing  40  handsome  seeds,  and  weighing, 
dry,  25^1^  grams.  In  these  trials  the  seedlings,  at  the 
time  of  unfolding  the  sixth  or  seventh  leaf,  after  consum* 
ing  the  nutriment  of  the  seeds,  manifested  remarkable 
symptoms  of  disturbed  nutrition,  growth  being  sup- 
pressed, and  the  foliage  becoming  yellow.  After  a  week 
or  two  the  plants  recovered  their  green  color,  began  to 
grow  again,  and  ^Dreserved  a  healthy  appearance  until 
mature.  Experiment  demonstrated  that  this  diseased 
state  was  not  affected  by  the  concentration  of  the  nour- 


304  HOW    CROPS   FEED. 

isliing  solution,  by  the  amount  of  free  acid  or  of  iron 
present,  nor  by  the  illumination.  Hampe  observed  that 
from  these  trials  it  seemed  that  the  plants^  v-hile  young , 
were  unable  to  assimilate  ammonia  or  did  so  with  diffi- 
culty^ hut  acquired  the  power  with  a  certain  age. 

In  1868,  Wagner  (Vs.  8t.,  XL,  288)  obtained  exactly 
the  same  results  as  Hampe.  He  found  also  that  a  maize- 
seedling,  allowed  to  vegetate  for  two  weeks  in  an  artificial 
soil,  and  then  placed  in  the  nutritive  solution,  with  phos- 
]_3hate  of  ammonia  as  a  source  of  nitrogen,  grew  nor- 
mally, without  any  symptoms  of  disease.  Wagner  ob- 
tained one  plant  weighing,  dry,  26^  1^  grams,  and  carrying 
48  ripe  seeds.  In  experiments  with  carbonate  of  ammonia, 
Wagner  obtained  the  same  negative  result  as  Beyer  had 
experienced  in  1866. 

Beyer  reports  ( Ys.  jSt.,  XI.,  267)  that  his  attempts  to 
nourish  the  oat-plant  in  solutions  containing  ammonia- 
salts  as  the  single  source  of  nitrogen  invariably  failed, 
although  repeated  through  three  summers,  and  varied  in 
several  ways.  Even  with  solutions  identical  to  those  in 
which  maize  grew  successfully  for  Hampe,  the  oat  seed- 
lings refused  to  increase  notably  in  weight,  every  precau- 
tion that  could  be  thought  of  being  taken  to  provide 
favorable  conditions.  It  is  not  impossible  that  all  these 
failures  to  supply  plants  with  nitrogen  by  the  use  of  am- 
monia-salts depend  not  upon  the  incapacity  of  vegetation 
to  assimilate  ammonia,  but  upon  other  conditions,  unfa- 
vorable to  growth,  which  are  inseparable  from  the  meth- 
ods of  experiment.  A  plant  growing  in  a  solution  or  in 
pure  quartz  sand  is  in  abnormal  circumstances,  in  so  far 
that  neither  of  these  media  can  exert  absorbent  power 
sufficient  to  remove  from  solution  and  make  innocuous  any 
substance  which  may  be  set  free  by  the  selec-tive  agency 
of  the  plant. 

Further  investigations  must  be  awaited  before  this 
point  can  be  definitely  settled.     It  -is,  however,  a  matter 


CONSTITTJTIOX    OF    THE    SOIL.  305 

of  little  j^ractical  importance,  since  ammonia  is  so  sparse- 
ly supplied  by  nature,  and  the  ammonia  of  fertilizers  is 
almost  invariably  subjected  to  the  conditions  of  speedy 
nitrification. 


CHAPTER     VI. 

TI-IE  SOIL  AS  A  SOURCE  OF  FOOD  TO  CROPS.— INGRE- 
DIENTS WHOSE  ELEMENTS  ARE  DERIVED  FROM 
ROCKS. 

§  1. 

GENERAL    VIEW    OF  THE    CONSTITUTION    OE   THE   SOIL  AS 
RELATED  TO  VEGETABLE  NUTRITION. 

Inertj  Active,  and  Reserve  Matters. — In  all  cases  the 
soil  consists  in  great  part  of  matters  that  are  of  no  direct 
or  present  use  in  feeding  the  plant.  The  chemical  nature 
of  this  inert  portion  may  vary  greatly  without  correspond- 
ingly influencing  the  fertility  of  the  soil.  Sand,  either 
quartzose,  calcareous,  micaceous,  feldspathic,  hornblendic, 
or  augitic ;  clay  in  its  many  varieties ;  chalk,  ocher  (oxide 
of  iron),  humus ;  in  short,  any  porous  or  granular  material 
that  is  insoluble  and  little  alterable  by  weather,  may  con- 
stitute the  mass  of  the  soil.  The  physical  and  mechanical 
characters  of  the  soil  are  chiefly  influenced  by  those  ingre- 
dients which  preponderate  in  quantity.  Hence  Ville  has 
quite  appropriately  designated  them  the  "mechanical 
agents  of  the  soil."  They  affect  fertility  princij^ally  as 
they  relate  the  plant  to  moisture  and  to  temperature. 
They  also  have  an  influence  on  crops  by  gradually  assum- 
ing more  active  forms,  and  yielding  nourishment  as  the 
result   of  chemical  changes.     In  general,  it  is  probable 


306  HOW    CHOPS    FEED. 

that  99  i^er  cent  and  more  of  the  soil,  exclusive  of  water, 
does  not  in  the  slightest  degree  contribute  directly  to  the 
support  of  the  present  vegetation  of  our  ordinary  field 
products. 

The  hay  crop  is  one  that  takes  up  and  removes  from 
the  soil  the  largest  quantity  of  mineral  matters  (ash- 
ingredients),  but  even  a  cutting  of  2^  tons  of  hay  car- 
ries off  no  more  than  400  lbs.  per  acre.  From  the 
data  given  on  page  158,  we  may  assume  the  weight  of 
the  soil  upon  an  acre,  taken  to  the  depth  of  one  foot, 
to  be  4,000,000  lbs.  The  ash-ingredients  of  a  heavy 
hay  crop  amount  therefore  to  but  one  ten-thousandth  of 
the  soil,  admitting  the  crop  to  be  fed  exclusively  by  the 
12  inches  next  the  surface.  Accordingly  no  less  than  100 
full  crops  of  hay  would  require  to  be  taken  off  to  consume 
one  per  cent  of  the  weight  of  the  soil  to  this  depth.  We 
confine  our  calculation  to  the  ash-ingredients  because  we 
have  learned  that  the  atmosphere  furnishes  the  main  sup- 
ply of  the  food  from  which  the  combustible  part  of  the 
crop  is  organized.  Should  we  spread  out  over  the  surface 
of  an  acre  of  rock  4,000,000  lbs.  of  the  purest  quartz 
sand,  and  sov*^  the  usual  amount  of  seed  upon  it,  maintain- 
ing it  in  the  proper  state  of  moisture,  etc.,  we  could  not 
produce  a  crop ;  we  could  not  even  recover  the  seed.  Such 
a  soil  v/ould  be  sterile  in  the  most  emphatic  sense.  But 
should  Tfe  incorporate  with  such  a  soil  a  few  thousand 
lbs.  of  the  mineral  ingredients  of  agricultural  plants,  to- 
gether with  some  nitrates  in  the  appropriate  combinations 
and  proportions,  we  should  bestow  fertility  upon  it  by  this 
addition  and  be  able  to  realize  a  crop.  Should  we  add  to 
our  acre  of  pure  quartz  the  ashes  of  a  hay  crop,  400  lbs., 
and  a  proper  quantity  of  nitrate  of  potash,  we  might  also 
realize  a  good  crop,  could  we  but  ensure  contact  of  the 
roots  of  the  plants  with  all  the  added  matters.  But  in 
this  case  the  soil  would  be  fertile  for  one  crop  only,  and 
after  the  removal  of  the  latter  it  would  be  as  sterile  as 


COXSTITUTIOX    OF   THE    SOIL.  307 

before.  We  gather,  then,  that  there  are  three  items  to  be 
regarded  in  the  simplest  view  of  the  chemical  comjDo- 
sition  of  the  soil,  viz.,  the  inert  mechanical  basis,  the 
presently  available  nutritive  ingredients,  and  the  reserve 
matters  from,  which  the  available  ingredients  are  supplied 
as  needed. 

In  a  previous  chapter  we  have  traced  the  formation  of 
the  soil  from  rocks  by  the  conjoint  agencies  of  mechanical 
and  chemical  disintegration.  It  is  the  perpetual  operation 
of  these  agencies,  especially  those  of  the  chemical  kind, 
which  serves  to  maintain  fertility.  The  fragments  of  rock, 
and  the  insoluble  matters  generally  that  exist  in  the  soil, 
are  constantly  suffering  decomposition,  whereby  the  ele- 
ments that  feed  vegetation  become  available.  What, 
therefore,  we  have  designated  as  the  inert  basis  of  the  soil, 
is  inert  for  the  moment  only.  From  it,  by  perpetual 
change,  is  preparing  the  available  food  of  crops.  Various 
attemipts  have  been  made  to  distinguish  in  fact  between 
these  three  classes  or  conditions  of  soil-ingredients ;  but 
the  distinction  is  to  us  one  of  idea  only.  We  cannot  realize 
their  separation,  nor  can  we  even  define  their  peculiar  con- 
ditions. We  are  ignorant  in  great  degree  of  the  power 
of  the  roots  of  plants  to  imbibe  their  food ;  we  are  equally 
ignorant  of  the  mode  in  which  the  elements  of  the  soil  are 
associated  and  combined ;  we  have,  too,  a  very  imperfect 
knowledge  of  the  chemical  transformations  and  decomposi- 
tions th?,t  occur  within  it.  We  cannot,  therefore,  dissect 
the  soil  and  d.ecide  what  and  how  much  is  immediately 
available,  and  what  is  not.  Furthermore,  the  soil  is  chem- 
ically so  complex,  and  its  relations  to  the  plant  are  so  com- 
plicated by  physical  and  physiological  conditions,  that  we 
may,  perhaps,  never  arrive  at  a  clear  and  unconfused  idea 
of  the  mode  by  which  it  nourishes  a  crop.  N'evertheless, 
what  we  have  attained  of  knowledge  and  insight  in  this 
direction  is  full  of  value  and  encouragement. 

Deporttaeat  of  t!ae  Soli  towards  Solyents. — When  we 


308  HOW    CROPS    PEED. 

put  a  soil  in  contact  with  water,  certain  matters  are  dis- 
solved in  this  liquid.  It  has  been  thought  that  the  sub- 
stances taken  up  by  water  at  any  moment  are  those  which 
at  that  time  represent  the  available  plant-food.  This  no- 
tion vf  as  based  upon  the  suj^position  that  the  plant  cannot 
feed  itself  at  the  roots  save  by  matters  in  solution.  Since 
Liebig  has  brought  into  prominence  the  doctrine  that  roots 
are  able  to  attack  and  dissolve  the  insoluble  ingredients 
of  the  soil,  this  idea  is  generally  regarded  as  no  longer 
tenable. 

Agam,  it  has  been  taught  that  the  ]'eserve  plant-food  of 
the  soil  is  represented  by  the  matters  which  acids  (hydro- 
chloric or  nitric  acid)  are  capable  of  bringing  into  solu- 
tion. This  is  true  in  a  certain  rough  sense  only.  The 
action  of  hydrochloric  or  nitric  acid  is  indeed  analogous 
to  that  of  carbonic  acid,  which  is  the  natural  solvent ;  but 
between  the  two  there  are  great  diiferences,  independent 
of  those  of  degree. 

Although  we  have  no  means  of  learning  with  positive 
accuracy  what  is  the  condition  of  the  insoluble  ingredients 
of  the  soil  as  to  present  or  remote  availability,  the  deport- 
ment of  the  soil  towards  water  and  acids  is  highly  in- 
structive, and  by  its  study  we  make  some  approach  to  the 
solution  of  this  question. 

Standards  of  S©lll])ility. — Before  proceeding  to  details, 
some  words  upon  the  limits  of  solubility  and  upon  what 
is  meant  by  soluble  in  water  or  in  acids  will  be  appropri- 
ate. The  terms  soluble  and  insoluble  are  to  a  great  de- 
gree relative  as  applied  to  the  ingredients  of  the  soil 
When  it  is  affirmed  that  salt  is  soluble  in  water,  and  that 
glass  is  insoluble  in  that  liquid,  the  meaning  of  the  state- 
ment is  plain ;  it  is  simply  that  salt  is  readily  recognized 
to  be  soluble  and  that  glass  is  not  ordinarily  perceived  to 
dissolve.  The  statement  that  glass  is  insoluble  is,  however, 
only  true  when  the  ordinary  standards  of  solubility  are  re- 
ferred to.     The  glass  bottle  Avhich  may  contain  water  for 


AQUEOUS    SOLUTION    OF   THE    SOIL.  309 

years  without  perceptibly  yielding  aught  of  its  mass  to  the 
liquid,  does,  nevertheless,  slowly  dissolve.  We  may  make 
its  solubility  perceptible  by  a  simple  expedient.  Pulver- 
ize the  bottle  to  the  finest  dust,  and  thus  extend  the  sur- 
face of  glass  many  thousand  or  million  times ;  weigh  the 
glass-powder  accurately,  then  agitate  it  for  a  few  minutes 
with  water,  remove  the  liquid,  dry  and  weigh  the  glass 
again.  We  shall  thus  find  that  the  glass  has  lost  several 
per  cent  of  its  original  weight  (Pelouze),  and  by  evapo- 
rating the  water,  it  will  leave  a  solid  residue  equal  in 
weight  to  the  loss  experienced  by  the  glass. 

§  2- 
AQUEOUS  SOLUTION  OF  THE  SOIL. 

The  soil  and  the  rocks  from  which  it  is  formed  would 
commonly  be  spoken  of  as  insoluble  in  water.  They  are, 
however,  soluble  to  a  slight  extent,  or  rather,  we  should 
say,  they  contain  soluble  matters. 

The  quantity  that  water  dissolves  from  a  soil  depends 
upon  the  amount  of  the  liquid  and  the  duration  of  its 
contact ;  it  is  therefore  necessary,  in  order  to  estimate 
properly  any  statements  respecting  the  solubility  of  the 
soil,  to  know  the  method  and-  conditions  of  the  experi- 
ment upon  which  such  statements  are  based. 

We  subjoin  the  results  of  A^arious  investigations  that 
exhibit  the  general  nature  and  amount  of  matters  soluble 
in  water. 

In  1852  Verdeil  and  Risler  examined  10  soils  from  the 
grounds  of  the  Institut  Agronomique^  at  Versailles.  In 
each  case  about  22  lbs.  of  the  fine  earth  were  mixed  with 
23ure  lukewarm  water  to  the  consistence  of  a  thin  pap, 
and  after  standing  several  hours  with  frequent  agitation 
the  water  was  poured  off;  this  process  was  repeated  to 
the  third  time.  The  clear,  faintly  yellow  solutions  thus 
obtained  v»^ere  evaporated  to  dryness,  and  the  residues 
were  analyzed  with  results  as  follows,  per  cent : 


310 


HOW    Cr.OFS    FEED. 


=6 

Per  cent  of  Ash. 

Name  of  Field, 

^,^- 

1.- 

'J?:! 

«• 

.^11 

=S 

! 

etc. 

^gs 

la^ 

•^^ 

II 

M 

.|?e 

1 

III 

§ 

§  e 

;^6^ 

N 

^b 

esb 

^^ 

Ohi; 

^ 

^b=S 

^. 

1 

Mall...  [Walk 

43.00 

57.00 

48.92  25.60 

4.27 

1.551     0.62 

7.63 

5.49 

3.77 

_ 

Pheasant 

70.50 

29.90 

31.49  35.29 

2.16 

0.47]  trace 

3.55 

13.67 

4.23 

__ 

Turf 

35.00165.00 

48.45    6.08 

2.75 

1.2l|     - 

6.19 

25.71 

5.06 



Q,ueen''s  Ave.. 

44.00 

55. 00 

43.75    6.08 

6.32 

2. 00,  trace 

14.45 

15.61 

4.13 



Kitchen  Gard. 

37.00 

63.00 

86. 60112. 35 

11.20 

trace    trace 

18.51 

19.60 

7.23 

trace 

Satory..[Galy 
Clay  soil  of 

33.00 

67.00 

18.70;24.25 

18.50 

3.72 

0.50 



21.60 

4.65 



48.00  52.00 

18.75  45.61 

3.83 

0.95 

1.55 

9.14 

5.00 

7.60 

7.60 

Lime  soil,  do. 

47.00 

53.00 

17. 21148. 50 

9.00 

trace 

— 

6.21 

5.50 



8.32 

Peatbog- 

46.00 

54.00 

24.43130.61 

0.92 

5.15 

trace 

6.06 

8.75 

7.45 



Sand  pit 

47.04 

52.06 

22. 31134.591  8.10 

1.02 

- 

4.05il5.58 

6.47 

— 

Here  we  notice  that  in  almost  every  instance  all  the 
mineral  ingredients  of  the  plant  were  extracted  from 
these  soils  by  water.  Only  magnesia  and  chlorine  are  in 
any  case  missing.  We  are  not  informed,  unfortunately, 
what  amount  of  soluble  matters  was  obtained  in  these 
experiments. 

We  next  adduce  a  number  of  statements  of  the  ^:)ro- 
portion  of  matters  which  water  is  capable  of  extracting 
from  earth,  statements  derived  from  the  analyses  of  soils 
of  widely  differing  character  and  origin. 

I.  Very  rich  soil  (excellent  for  clover)  from  St,  Martin's, 
Upper  Austria,  treated  with  six  times  its  quantity  of  cold 
water  (Jarriges). 

II.  Excellent  beet  soil  (but  clover  sick)  from  Schlan- 
staedt,  Silesia,  treated  with  5  times  its  quantity  of  cold 
water  (Jarriges). 

III.  Fair  wheat  soil,  Seltendorf,  Silesia,  treated  with  5 
times  its  weight  of  cold  water  (Peters). 

lY.  Inferior  wheat  soil  from  Lampersdorf,  Silesia — 
5-fold  quantity  of  water  (Peters). 

Y.  Good  wheat  soil,  Warwickshire,  Scotland — 10-fold 
quantity  of  hot  water  (Anderson). 

YI.  Garden  soil,  Cologne — 3-fold  amount  of  cold  water 
(Grouvcn). 


AQUEOUS    SOLUTION    OF   THE    SOIL. 


311 


Vn.  Garden  soil,  Heidelberg — 3-fold  amount  of  cold 
water  (Grouven). 

Yni.  Poor,  sandy  soil,  Bickendorf — 3-fold  amount  of 
cold  water  (Grouven). 

IX.  Clay  soil,  beet  field,  Liebesnitz,  Bohemia,  extract- 
ed with  9.6  times  its  weight  of  water  (R.  Hoffmann). 

X.  Peat,  Meronitz,  Bohemia,  extracted  with  16  times 
its  weight  of  water  (R.  Hoffmann). 

XI.  Peaty  soil  of  meadow,  extracted  with  8  times  its 
weight  of  water  (R.  Hoffoaann). 

XH.  Sandy  soil,  Moldau  Valley,  Bohemia,  treated  with 
twice  its  weight  of  water  (R.  Hoffmann). 

Xin.   Salt  meadow,  Stollhammer,  Oldenburg  (Harms). 
XIY.  Excellent  beet  soil,  Magdeburg  (Hellriegel). 

XV.  Poor  beet  soil,  but  good  grain  soil,  Magdeburg 
(Hellriegel). 

XVI.  Experimental  soil,  Ida-Marienhiitte,  Silesia,  treat- 
ed with  2|-  times  its  weight  of  cold  water  (Kiillenberg). 

XVII.  Soil  from  farm  of  Dr.  Geo.  B.  Loring,  Salem, 
Mass.,  treated  with  twice  its  weight  of  water  (W.  G. 
Mixter). 

MATTERS    DISSOLVED    BY    WATER    FROM    100,000   PARTS    OF 
VARIOUS  SOILS. 


1 

1 

1 

j 

1 

1 

1 

b1§ 

1 

I 

18 

2 

13 

8 

2 

1 

5 

11 

5 

53 

134 

n 

5 
6 

21/2 
1 

3 

4 

514 
4 

trace 

trace 
trace 

trace 
1 

41/4 
2 

fA 

24 
23 

51 

Ill 

43 

IV.  .  . 

10 
34 

trace 

7 

1 

8 

2 
13 

— 

trace 

7 

1 
9 

11 

22 

3 

18 
36 

46 

V 

136 

VI 

17 

8 

9 

7!4 

5 

21/0 

61/2 

131/i 

1 

-22 

87 

VII 

23 

1% 

7 

41/, 

1% 

1% 

1 

38 

2 

30 

110 

VIII 

8 

¥2 

/4 

3% 

trace 

1 

15/2 

20 

— 

10 

45 

IX 

3314 

3i/„ 

4v„ 

9 

5 

31/4 

18 

trace 



70 

147 

X 

164 

11 

47 

12 

trace 

33 

302 

trace 

77 

449 

1095 

XI 

92 

1 

44 

21/0 

21 
2 

24 
1 

trace 
trace 

trace 
trace 

11 
trace 

1 
trace 

2 

230 
33 

425 

XII 

391/4 

XIII 

79 

43 

16 

476 

— 

407 

144 

58 

— 

170 

1393 

XIV 

19 

3 

3 

5 

1 

4 

4 

20 

3 

88 

150 

XV 

26 

5 

3 

4 

1 

5 

3 

15 

2 

83 

147 

XVI 

61/, 

2 

1 

3 

V2 

51/, 

3K 

12 

7 

12 

53 

XVII 

8 

2 

61/2 

1 

Mm 

71/2 

m 

17 

12 

551/$. 

312  HOW    CKOPS    FEED. 

The  foregoing  analyses  (all  the  author  has  access  to 
that  are  sufficiently  detailed  for  the  purpose)  indicate 

1.  That  the  quantity  of  soluble  matters  is  greatest — 400 
to  1,400  in  100,000— in  wet,  peaty  soils  (X,  XI,  XIII), 
though  their  aqueous  solutions  are  not  rich  in  some  of  the 
most  important  kinds  of  plant-food,  as,  for  example,  phos- 
phoric acid. 

2.  That  poor,  sandy  soils  (VIII,  XII)  yield  to  water  the 
least  amount  of  soluble  matters, — 40  to  45  in  100,000. 

3.  That  very  rich  soils,  and  rich  soils  especially  when 
recently  and  heavily  manured  as  for  the  hop  and  beet 
crops  (I,  II,  V,  VI,  VII,  IX,  XIV,  XV,  XVI),  yield,  in 
general,  to  water,  a  larger  proportion  of  soluble  matters 
than  poor  soils,  the  quantity  ranging  in  the  instances  be- 
fore us  from  50  to  150  parts  in  100,000. 

4.  It  is  seen  that  in  most  cases  phosphoric  acid  is  not 
present  in  the  aqueous  extract  in  quantity  sufficient  to  be 
estimated;  in  some  instances  other  substances,  as  mag- 
nesia, chlorine,  and  sulphuric  acid,  occur  in  traces  only. 

5.  In  a  num.ber  of  cases  essential  elements  of  plant- 
food,  viz.,  phosphoric  acid  and  sulphuric  acid,  are  wanting, 
or  their  presence  was  overlooked  by  the  analyst. 

Compositioa  of  Drain-Water,— Before  further  discus- 
sion of  the  above  data,  additional  evidence  as  to  the  kind 
and  extent  of  aqueous  action  on  the  soil  will  be  adduced. 
The  water  of  rains,  falling  on  the  soil  and  slowly  sinking 
through  it,  forms  solutions  on  the  grand  scale,  the  study 
of  which  must  be  instructive.  Such  solutions  are  easily 
gathered  in  their  full  strength  from  the  tiles  of  thorough- 
drained  fields,  when,  after  a  period  of  dry  weather,  a  rain- 
fall occurs,  sufficient  to  saturate  the  ground. 

Dr.  E.  Wolff,  at  Moeckern,  Saxony,  made  two  analyses 
of  the  water  collected  in  the  middle  of  May  from  newly 
laid  tiles,  when,  after  a  period  of  no  flow,  the  tiles  had 


AQUEOUS    SOLUTION    OF    THE    SOIL. 


;i3 


been  running  full  for  several  hours  in  consequence  of  a 
heavy  rain.     The  soil  was  of  good  quality.     He  found : 

IN  100,000   PARTS   OF   DRAIN-WATER. 


Eye  field. 

Meadow. 

Organic  matters, 
Carbonate  of  lime, 

2.6 

31.9 

3.2 
4.4 

*'            "  magnesia, 
♦'           "  potash, 
"  soda, 

3.1 
0.3 
1.9 

1.4 
0.5 
L4 

Chloride  of  sodium, 

2.3 

trace 

Sulphate  of  potash, 
Alumina,                        ) 
Oxide  of  iron,.              f 

1.2 
0.8 

trace 
0.6 

Silica, 

0.7 

0.4 

Phosphoric  acid. 

trace 

1.9 

34.8 


13.8 


Prof.  "Way  has  made  a  series  of  elaborate  examinations 
on  drain-waters  furnished  by  Mr.  Paine,  of  Farnham, 
Surrey.  The  waters  were  collected  from  the  pipes  (4-5 
ft.  deep)  of  thorough-drained  fields  in  December,  1855, 
and  in  most  cases  were  the  first  flow  of  the  ditches  after 
the  autumn  rains.  The  soils,  with  exception  of  7  and  8, 
were  but  a  few  years  before  in  an  impoverished  condition, 
but  had  been  brought  up  to  a  high  state  of  fertility  by  ma- 
nuring and  deep  tillage.    {Jour.  Roy.  Ag.  Soc,  XVII,  133.) 

IN  100,000  PARTS  OF  DRAIN- WATER. 


1 
WJieat 
fdd. 

2 
HoiJ 
field- 

3 

Hoj) 
field. 

4 
Wheat 
field. 

Wheat 
field. 

6 
field. 

7 
fi£ld. 

Potash 

Soda 

trace 
1.43 
6.93 

o.9r 

0.59 
1.35 
1.00 
2.35 
trace 

10.24 
0.025 

10.00 

trace 
3.10 

10.24 
3.31 
0.07 
0.64 
1.57 
7.35 
0.17 

21.(15 
0.025 

10.57 

0.03 
3.23 
8.64 
3.54 
0.14 
0.78 
1.84 
6.28 
trace 
18.17 
0.025 
17.85 

0.07 

1.24 

2.23 

0.58 

none 

1.71 

1.16 

2.44 

trace 

2.78 

0.017 

8.00 

trace 

2.03 

3.60 

0.30 

1.85 

2.57 

1.80 

1.84 

0.11 

4.93 

0.025 

8.14 

0.31 
2.00 
8  31 
1.33 
0.50 
0.93 
1.73 
4.45 
0.09 
11.50 
0.025 
8.28 

trace 
4.57 

18.50 

Ma^'nesia                   

3.57 

Oxfde  of  iron  and  alumina. 
Silica                      

0.71 
1.21 

Chlorine .. 

3.74 

13.58 

Phosphoric  acid               .... 

0.17 

16.35 

Ammonia 

Soluble  organic  matter 

0.009 
10.57 

Total 

34.885 

58.095 

60.525 

21.227 

27.195 

39.455 

72.979 

14 


814  HOW    CROPS    FEED. 

Krocker  has  also  published  analyses  of    drain-waters 
collected  in  summer  from  poorer  soils.     He  obtained 


IN  100,000  PARTS : 

a 

b 

c 

d 

e 

/ 

Organic  matters, 

2.0 

2.4 

1.6 

0.6 

6.3 

5.6 

Carbonate  of  lime, 

8.4 

8.4 

12.7 

7.9 

7.1 

8.4 

Sulphate  of  lime. 

20.8 

21.0 

11.4 

1.7 

7.7 

7.2 

Nitrate  of  lime, 

0.2 

0.2 

0.1 

0.2 

0.2 

0.2 

Carbonate  of  magnesia, 

7.0 

6.9 

4.7 

2.7 

2.7 

1.6 

Carbonate  of  iron. 

0.4 

0.4 

0.4 

0.2 

0.2 

0.1 

Potash, 

0.2 

0.2 

0.2 

0.2 

0.4 

0.6 

Soda, 

1.1 

1.5 

1.3 

1.0 

0.5 

0.4 

Chloride  of  sodium, 

0.8 

0.8 

0.7 

0.3 

0.1 

0.1 

Silica, 

O.T 

0.7 

0.6 

0.5 

0.6 

0.5 

Total,  42.1         42.5  33.7  15.3  25.8  24.7 

Krocker  remarks  {Jour,  far  Fraht.  Chem.^  60-466)  that 
phosphoric  acid  could  be  detected  in  all  these  waters, 
though  its  quantity  was  too  small  for  estimation. 

a  and  h  are  analyses  of  water  from  the  same  drains — a 
gathered  April  1st,  and  h  May  1st,  1853 ;  c  is  from  an  ad- 
joining field;  c?,  from  a  field  where  the  drains  run  con- 
stantly, where,  accordingly,  the  drain-water  is  mixed  witli 
spring  water ;  e  and  f  are  of  water  running  from  the  sur- 
face of  a  field  and  gathered  in  the  furrows. 

Lysimeter-Water. —  Entirely  similar  results  were  ob- 
tained by  Zoller  in  the  analysis  of  water  which  was  col- 
lected in  the  Lysimeter  of  Fraas.  The  lysimeter  *  con- 
sists of  a  vessel  with  vertical  sides  and  open  above,  the 
upper  23art  of  which  contains  a  layer  of  soil  (in  these  ex- 
periments 6  inches  deep)  supported  by  a  perforated  shelf, 
while  below  is  a  reservoir  for  the  reception  of  water. 
The  vessel  is  imbedded  in  the  ground  to  within  an  inch  of 
its  upper  edge,  and  is  then  filled  from  the  diaphragm  up 
v>^ith  soil.  In  this  condition  it  remains,  the  soil  in  it  being- 
exposed  to  the  same  influences  as  that  of  the  field,  while 
the  water  which  percolates  the  soil  gathers  in  the  reservoir 


Measurer  of  solution. 


AQUEOUS    SOLUTION    OF   THE    SOIL.  315 

below.  Dr.  Zoller  analyzed  the  water  that  was  thus  col- 
lected from  a  number  of  soils  at  Munich,  in  the  half  year, 
April  7th  to  Oct.  7th,  1857.     He  found 

IN  100,000  OF  LYSIMETEE-WATER : 


Potash, 

0.65 

0.24 

0.20 

0.55 

0.38 

Soda, 

0.71 

0.56 

0.74 

2.37 

0.60 

Lime, 

14.58 

5.76 

7.08 

6.84 

9.23 

Magnesia, 

2.05 

0.89 

0.13 

0.29 

0.51 

Oxide  of  iron. 

0.01 

0.03 

0.83 

0.57 

0.43 

Chlorine, 

5.75 

0.95 

2.08 

3.94 

3.53 

Phosphoric  acid. 

0.22 

— 

— 

— 

— 

Sulphuric  acid, 

1.75 

2.71 

2.78 

2.93 

3.35 

Silica, 

1.04 

1.13 

1.75 

0.95 

0.93 

Organic  matter,  w 

ith 

some 

[-20.47 

12.59 

13.67 

12.08 

10.19 

nitric  and  carbonic  acids, 

Total,  47.23  25.46  29.26  30.52  29.15 

The  foregoing  analyses  of  drain  and  lysimeter-water 
exhibit  a  certain  general  agreement  in  their  results. 
They  agree,  namely,  in  demonstrating  the  presence  in  the 
soil-water  of  all  the  mineral  food  of  the  plant,  and  while 
the  figures  for  the  total  quantities  of  dissolved  matters 
vary  considerably,  their  average,  36J  parts  to  100,000  of 
water,  is  probably  about  equally  removed  from  the  ex- 
tremes met  with  on  the  one  hand  in  the  drainage  from  a 
very  highly  manured  soil,  and  on  the  other  hand  in  that 
where  the  soil-solution  is  diluted  with  rain  or  spring  water 

It  must  not  be  forgotten  that  in  the  analyses  of  drain- 
age water  the  figures  refer  to  100,000  parts  of  water ; 
whereas,  in  the  anjalyses  on  p.  311,  they  refer  to  100,000 
parts  of  soil,  and  hence  the  two  series  of  data  cannot  be 
directly  compared  and  are  not  necessarily  discrepant. 

Is  Soil-Water  destitute  ©f  certain  Nutritive  Matters  ? 

— We  notice  that  in  the  natural  solutions  which  flow  off 
from  the  soil,  phosphoric  acid  in  nearly  every  case  exists 
in  quantity  too  minute  for  estimation ;  and  when  estimat- 
ed, as  has  been  done  in  a  number  of  instances,  its  propor- 
tion does  not  reach  2  parts  in  100,000.  This  fact,  together 
with  the  non-appearance  of  the  same  substance  and  of  oth- 


316  now  CROPS  feed. 

er  nutritive  elements,  viz.,  chlorine  and  sulphuric  acid,  in 
the  Table,  p. 311,  leads  to  the  question,  May  not  the  aqueous 
solution  of  the  soil  be  altogether  lacking  in  some  es- 
sential kinds  of  mineral  plant-food  in  certain  instances  ? 
May  it  not  happen  in  case  of  a  rather  poor  soil  that  it  will 
support  a  moderate  crop,  and  yet  refuse  to  give  up  to 
water  all  the  ingredients  of  that  crop  that  are  derived 
from  the  soil  ? 

The  weight  of  evidence  supports  the  conclusion  that 
water  is  capable  of  dissolving  from  the  soil  all  the  sub- 
stances that  it  contains  which  serve  as  the  food  of  plants. 
The  absence  of  one  or  several  substances  in  the  analytical 
statement  would  seem  to  be  no  proof  of  their  actual  ab- 
sence in  the  solution,  but  indicates  simply  that  the  sub- 
stance was  overlooked  or  was  too  small  for  estimation  by 
the  common  methods  of  analysis  in  the  quantity  of  solu- 
tion which  the  experimenter  had  in  hand.  It  would  ap- 
pear probable  that  by  employing  enough  of  the  soil  and 
enough  water  in  extracting  it,  solutions  would  be  easily 
obtained  admitting  of  the  detection  and  estimation  of  ev- 
ery ingredient.  Knop,  however,  asserts  (  Chem.  Central- 
hlatt,  1864,  168)  that  he  has  repeatedly  tested  aqueous 
solutions  of  fruitful  soils  for  phosphoric  acid,  employing 
the  soils  in  quantities  ranging  from  2  to  22  lbs.,  and  water 
in  similar  amounts,  without  in  any  case  finding  any  traces 
of  it.  On  the  other  hand  Schulze  mentions  having  inva- 
riably detected  it  in  numerous  trials ;  and  Yon  Babo,  in 
the  examination  of  seven  soils,  found  phosphoric  acid  in 
every  instance  but  one,  which,  singularly  enough,  was 
that  of  a  recently  manured  clay  soil.  In  no  case  did  he 
fail  to  detect  lime,  potash,  soda,  sulphuric  acid,  chlorine, 
and  nitric  acid ;  magnesia  he  did  not  look  for.  (Hoff- 
mann''s  Jahreshericht  der  Ag.  Chem.,  I.  IT.) 

So  TIeiden,  in  answer  to  Knop's  statement,  found  and 
estimated  phosphoric  acid  in  four  instances  in  proportions 


AQUEOUS    SOLUTIO^r    OF   THE    SOIL.  317 

ranging  from  2  to  6  parts  in  100,000  of  soil.     {Jahreshe- 
richt  der  Ag.  Chem.^  1865,  p.  34.) 

It  should  be  remarked  that  Knop's  failure  to  find  phos- 
phoric acid  may  depend  on  the  (uranium)  method  he  em- 
ployed, a  method  different  from  that  commonly  used. 

Can  tlie  Soil-water  supply  Crops  witli  Food]  —  As- 
suming, then,  that  all  the  soil-food  for  plants  exists  in  solu- 
tion in  the  water  of  the  soil,  the  question  arises.  Does  the 
water  of  the  soil  contain  enough  of  these  substances  to 
nourish  crops  ?  In  case  of  very  fertile  or  highly  manured 
fields,  this  question  without  doubt  should  be  answered  af- 
firmatively. In  respect  of  poor  or  ordinary  soils,  how- 
ever, the  answer  has  been  for  the  most  part  of  late  years 
in  the  negative.  While  to  decide  such  a  question  is,  per- 
haps, impossible,  a  closer  discussion  of  it  may  prove  ad- 
vantageous. 

Russell  {Journal  Highland  and  Ag.  8oc.,  ISTew  Series, 
Yol.  8,  p.  534)  and  Liebig  {Ann,  d.  Chem.  u.  Pharm.^  CY, 
138)  were  the  first  to  bring  prominently  forward  the  idea 
that  crops  are  not  fed  simply  from  aqueous  solutions.  Dr. 
Anderson,  of  Glasgow,  presents  the  argument  as  follows 
(his  Ag.  Chemistry^  p.  113) : 

"  In  order  to  obtain  an  estimate  of  the  quantity  of  the 
substances  actually  dissolved,  we  shall  select  the  results 
obtained  *  by  Way.  The  average  rain-fall  in  Kent,  where 
the  waters  he  examined  were  obtained,  is  25  inches.  Now, 
it  appears  that  about  two-fifths  of  all  the  rain  which  falls 
escapes  through  the  drains,  and  the  rest  is  got  rid  of  by 
evaporation.!  An  inch  of  rain  falling  on  an  English  acre 
weighs  rather  more  than  a  hundred  tons;  hence  iii  the 
course  of  a  year,  there  must  pass  off  by  the  drains  about 
1,000  tons  of  drainage  water,  carrying  with  it,  out  of  the 
reach  of  plants,  such  substances  as  it  has  dissolved,  and 


*  On  drain-waters,  see  p.  313. 

t  From  Parke's  measurements,  Jour.  Roy.  Ag.  Soc,  Eng.,  Vol,  XVII,  p.  127. 


818  HOW    CROPS    FEED. 

1,500  tons  must  remain  to  give  to  the  plant  all  that  it  holds 
in  solution.  These  1,500  tons  of  water  must,  if  they  have 
the  same  composition  as  that  which  escapes,  contain  only- 
two  and  a  half  pounds  of  potash  and  less  than  a  pound 
of  ammonia.  It  may  be  alleged  that  the  water  which  re- 
mains lying  longer  in  contact  with  the  soil  may  contain  a 
larger  quantity  of  matters  in  solution ;  but  even  admit- 
ting this  to  be  the  case,  it  cannot  for  a  moment  be  sup- 
posed that  they  can  ever  amount  to  more  than  a  very 
small  fraction  of  what  is  required  for  a  single  crop." 

The  objection  to  this  conclusion  which  Anderson  al- 
ludes to  above,  but  which  he  considers  to  be  of  little  mo- 
ment, is,  perhaps,  a  serious  one.  The  soil  is  saturated 
with  water  sufficiently  to  cause  a  flow  from  drains  at  a 
depth  of  4  to  5  ft.,  for  but  a  small  part  of  the  grow- 
ing season.  The  Indian  corn  crop,  for  example,  is  planted 
in  'New  England  in  the  early  part  of  June,  and  is  harvest- 
ed the  first  of  October.  During  the  four  months  of  its 
growth,  the  average  rain-fall  is  not  enough  to  make  a  flow 
from  drains  for  more,  perhaps,  than  one  day  in  seven. 
During  six-sevenths  of  the  time,  then,  there  is  a  current  of 
water  ascending  in  the  soil  to  supply  the  loss  by  evapora- 
tion at  the  surface.  In  this  way  the  solution  at  the  sur- 
face is  concentrated  by  the  carrying  upward  of  dissolved 
matters.  A  heavy  rain  dilutes  this  solution,  not  having 
time  to  saturate  itself  before  reaching  the  drains.  Ac- 
cordingly we  find  that  the  quantity  of  matters  dissolved 
by  water  acting  thoroughly  on  the  surface  soil  is  greater 
than  that  washed  out  by  an  equal  amount  of  drain- water ; 
at  least  such  is  the  conclusion  to  be  gathered  from  the 
experiments  of  Eichhorn  and  Wunder. 

These  chemists  have  examined  the  solution  obtained  by 
leaving  soil  in  contact  with  just  sufficient  water  to  saturate 
it  for  a  number  of  days  or  weeks.     (  Vs.  St.,  II,  pp.  107- 

111.) 

The  soil  examined  by  Eichhorn  was  from  a  garden  near 


AQUEOUS    SOLUTION    OF    THE    SOIL.  319 

Bonu,  Prussia,  not  freshly  manured,  and  was  treated  with 
about  one-third  its  weight  (36.5  per  cent)  of  cold  water 
for  ten  days. 

Wunder  employed  soil  from  a  field  of  the  Experiment 
Station,  Chemnitz,  Saxony.  This  soil  had  not  been  re- 
cently manured,  and  was  of  .rather  inferior  quality  (yield- 
ed 15  bushels  wheat  per  acre,  English).  It  was  also 
treated  with  about  one-third  its  weight  (34.5  per  cent)  of 
water  for  four  weeks. 

The  solutions  thus  procured  contained  in  100,000  parts, 

Bonn.  Chemnitz. 


Silica, 

4.80 

2.57 

Sulphuric  acid, 

10.02 

Phosphoric  acid, 

3.10 

traces 

Oxide  of  iron  and  alumina, 

trace 

1.17 

Chloride  of  sodium, 

5.86 

4.76 

Lime, 

12.80 

8.36 

Magnesia, 

3.84 

3.74 

Potash, 

11.54 

0.75 

Soda, 

1.10 

3.04 

If  we  assume  with  Anderson  that  1,500  tons  (=  3,360,000 
lbs.)  of  water  remain  in  these  soils  to  feed  a  crop,  and  that 
this  quantity  makes  solutions  like  those  whose  composition 
is  given  above,  we  have  dissolved  (in  pounds  per  English 
acre)  from  the  soil  of 


Bonn. 

Chemnitz. 

Silica, 

181 

86 

Sulphuric  acid. 

343 

— 

Phosphoric  acid, 

104 

9 

Oxide  of  iron  and  alumina, 

39 

Chloride  of  sodium, 

197 

160 

Lime, 

430 

281 

Magnesia, 

129 

126 

Potash, 

387 

25 

Soda, 

37 

102 

These  results  differ  widely  from  those  based  on  the  com- 
position of  drain-water.  Eichhorn,  by  a  similar  calcula- 
tion, was  led  to  the  conclusion  that  the  soil  he  operated 
with  was  capable  of  nourishing  the  heaviest  crops  with 


320  HOW    CROPS    FEED. 

its  aqueous  solution.  Wunder,  on  the  contrary,  calculat- 
ed that  the  Chemnitz  soil  yields  insufficient  matters  for 
the  ordinary  amount  of  vegetation ;  and  we  see  that  as 
respects  potash,  the  wants  of  grass  and  root  crops  could 
not  be  satisfied  with  the  quantities  in  our  computation, 
while  sulphuric  acid  and  phosphoric  acid  are  nearly  or  en- 
tirely wanting.  We  do  not,  however,  regard  such  calcu- 
lations as  decisive,  either  one  way  or  the  other.  The 
quantity  of  water  which  may  stand  at  the  actual  service 
of  a  crop  is  beyond  our  power  to  estimate  with  anything 
like  certainty.  Doubtless  the  amount  assumed  by  Ander- 
son is  too  large,  and  hence  the  calculations  relative  to  the 
Bonn  and  Chemnitz  soils  as  above  interpreted,  convey  an 
exaggerated  notion  of  the  extent  of  solution. 

Proper  Conceatratloa  of  Plant-Food.  — Let  us  next 
inquire  what  strength  of  solution  is  necessary  for  the  sup- 
port of  plants. 

As  has  been  shown  by  ISTobbe  ( Vs,  St.,  VIII,  p.  337), 
Birner  &  Lucanus  (  Vs.  St.,  VIII,  p.  134),  and  Wolff  (  Vs. 
St.,  YIII,  p.  192),  various  agricultural  plants  flourish  to 
extraordinary  perfection  when  their  roots  are  immersed  in 
a  solution  containing  about  one  part  of  ash-ingredients 
(together  with  nitrates)  to  1,000  of  water. 

The  solutions  they  employed  contained  the  following 
substances  in  the  proportions  stated  (approximately)  be- 
low: 


In  100,000  parts  of  Water. 

Nobbe. 

Birner  &,  Lucanus. 

Wolff. 

Lime, 

18 

19 

19 

Magnesia, 

3 

6>^ 

2X 

Potash, 

31 

16 

16 

Phosplioric  acid, 

7 

24 

14 

Chlorine, 

21 

none 

2 

Sulphuric  acid, 

6 

13 

4 

Oxide  of  iron, 

K 

y^ 

K 

Nitric  acid. 

31K 

36 

51 

116  115  109 

Nobbe  found  further  that  the  vigor  of  vegetation  in  his 


AQUEOUS    SOLUTION    OF   THE    SOIL.  321 

solution  was  diminislied  either  by  reducing  the  proportion 
of  sohd  matters  below  0.5,  or  increasing  it  to  2  parts  in 
1,000  of  water.  The  proper  dilution  of  the  food  of  plants 
for  most  vigorous  growth  and  most  perfect  development 
is  thus  approximately  indicated. 

We  notice,  however,  considerable  latitude  as  regards 
the  proportions  of  some  of  the  most  important  ingredients 
which  are  usually  present  in  least  quantity  in  the  aqueous 
solution  of  the  soil.  Thus,  phosphoric  acid  in  one  case  is 
thrice  as  abundant  as  in  the  other.  We  infer,  therefore, 
that  the  minimum  limit  of  the  individual  ingredients  is 
not  fixed  by  the  above  experiments,  especially  not  for  or- 
dinary growth. 

Birner  and  Lucanus  communicate  other  results  ( Vs.  St., 
YIIL,  p.  154),  which  throw  much  light  on  the  question  un- 
der discussion.  They  compared  the  growth  of  the  oat  plant, 
when  nourished  respectively  by  a  rich  garden  soil,  by 
ordinary  cultivated  land,  by  a  solution  the  composition 
of  which  is  given  above,  and  lastly  by  a  natural  aqueous 
solution  of  soil,  viz.,  a  vjell-water.  Below  is  a  statement 
of  the  weight  in  grams  of  an  average  plant,  produced  in 
these  various  media,  as  well  as  that  of  the  grain  yielded 
by  it. 

Dry   crops   compared 

Weight  of  aver-  Weight  of  with  seed,  the  latter 

a^e  plant,  dry.  dry  Graiu.  taken  as  unity. 

Garden 5.27                       1.23  193 

Field 1.75                       0.63  64 

Solution 3.75                       1.53  137 

Well-water 2.91                       1.25  106 

We  gather  from  the  above  figures  that  well-water,  in 
quantities  of  one  quart  for  each  plant,  renewed  weekly, 
gave  a  considerably  heavier  plant,  straw,  and  grain,  than 
a  field  under  ordinary  culture  ;  the  yield  in  grain  being 
double  that  of  the  latter,  and  equal  to  that  obtained  in  a 
rich  garden  soil. 
14* 


322  HOW    CROPS    FEED. 

The  analysis  of  the  well-water  shows  that  the  nutritive 
solution  need  not  contain  the  food  of  plants  in  greater 
proj^ortion  than  occurs  in  the  aqueous  extract  of  ordinary 

soils. 

The  well-water  contained,  in  100,000  parts. 

Lime,          -         -          -         -         -  15.14 

Magnesia,         -        -         -         -         -  1.53 

Potash,         -          -          -          -          .  2.13 

Phosphoric  acid,         -        -        -        -  0.16 

Sulphuric  acid,        -        -        -        -  7.45 

Mtric  acid, 6.02 

We  thus  have  demonstration  that  a  solution  containing 
but  one-and-a-half  parts  of  phosphoric  acid  to  ten  million 
of  water  is  competent,  so  far  as  this  substance  is  concern- 
ed, to  support  a  crop  bearing  twice  as  much  grain  as  an 
ordinary  soil  could  produce  under  the  same  circumstances 
of  weather.  Do  we  thus  reach  the  limit  of  dilution  ? 
We  cannot  answer  for  agricultural  plants,  but  in  case  of 
some  other  forms  of  vegetation,  the  reply  is  obvious  and 
striking. 

Various  species  of  Fucus^  Laminaria^  and  other  ma- 
rine plants,  contain  iodine  in  notable  quantities.  This 
element,  so  much  used  in  photography  and  medicine,  is 
made  exclusively  from  the  ashes  of  these  sea-weeds,  one 
establishment  in  Glasgow  producing  35  tons  of  it  annu- 
ally. The  iodine  must  be  gathered  from  the  water  of  the 
ocean  in  which  these  plants  vegetate,  and  yet,  although 
the  starch-test  is  so  delicate  that  one  part  of  iodine  can 
be  detected  when  dissolved  in  300,000  parts  of  water,  it 
is  not  possible  to  recognize  iodine  in  the  "  bitterns  "  which 
remain  when  sea-water  is  concentrated  to  the  one-hund- 
reth  of  its  original  bulk,  so  that  its  proportion  must  be 
less  than  one  part  in  thirty  millions  of  water !  ( Otto's 
Lehrhuch  der  Chemie^  4:te,  Avjf.^  pp.  743-4.) 


AQUEOUS    SOLUTION    OF    THE    SOIL.  323 

Mode  wliereby  dilute  soMioM  may  nourish  Crops. — 

There  are  other  considerations  which  may  enable  us  to 
reconcile  extreme  dilution  of  the  nutritive  liquid  of  the 
soil,  with  the  conveyance  by  it  into  the  plant  of  the  req- 
uisite quantity  of  its  appropriate  food.  It  is  certain 
that  the  amount  of  matters  found  in  solution  at  any 
given  moment  in  the  water  of  the  soil  by  no  means  repre- 
sents its  power  of  supplying  nourishment  to  vegetation. 

If  the  water  which  has  saturated  itself  with  the  solu- 
ble matters  of  the  soil  be  deprived  of  a  portion  or  all  of 
these  matters,  as  it  might  be  by  the  absorptive  action  of 
the  roots  of  a  j)lant,  the  water  would  immediately  act 
anew  upon  the  soil,  and  in  time  would  dissolve  another 
similar  quantity  of  the  same  substance  or  substances,  and 
these  being  taken  up  by  plants,  it  would  again  dissolve 
more,  and  so  on  as  long  and  to  such  an  extent  as  the  soil 
itself  would  admit.  In  other  words,  the  same  water  may 
act  over  and  over  again  in  the  soil,  to  transfer  from  it  to 
the  crop  the  needful  soluble  matters.  It  has  been  shown 
that  the  substances  dissolved  in  water  may  diffuse  through 
animal  and  vegetable  tissues  independently  of  each  other, 
and  independently  of  the  water  itself.    (H.  C.  G.,  p.  340.) 

Deportment  of  the  Soil  to  renewed  portions  of  Water. 
— ^It  remains  to  satisfy  ourselves  that  the  soil  is  capable 
of  yielding  soluble  matters  continuously  to  renewed  por- 
tions of  water.  The  only  observations  on  this  point  that 
the  writer  is  acquainted  with  are  those  made  by  Schulze 
and  Ulbricht.  Schulze  experimented  on  a  rich  soil  from 
Goldberg,  in  Mecklenburg  ( Vs.  St.,  YL,  411).  This  soil, 
in  a  quantity  of  1,000  grams  (=  2.2  lbs.)  was  .slowly 
leached  with  pure  water,  so  that  one  liter  (=  1.056  quart) 
of  liquid  passed  it  in  24  hours.  The  extraction  was  con- 
tinued during  six  successive  days,  and  each  portion  was 
separately  examined  for  total  matters  dissolved,  and  for 
phosphoric  acid,  which  is,  in  general,  the  least  soluble  of 
the  soil-ingredients. 


324 


HOW    CROPS    FEED. 


The  results  were  as  follows,  for  1,000  parts  of  extract, 


Portion  of 

Total 

Organic 

aqueous 

matters 

and 

Phosphoric 

extract. 

dissolved. 

volatile. 

Inorganic. 

acid. 

1 

0.535 

0.340 

0.195 

0.0056 

2 

0.120 

0.057 

0.063 

0.0082 

3 

0.261 

0.101 

0.160 

O.OOSS 

4 

0.203 

0.083 

0.120 

0.0075 

5 

0.260 

0.082 

0.178 

0.0069 

6 

0.200 

0.077 

0.123 

0.0044 

1.579 


0.740 


0.839 


0.0414 


We  see  that  each  successive  extraction  removed  from 
the  soil  a  scarcely  diminished  quantity  of  mineral  mat- 
ters, including  phosphoric  acid.  In  case  of  a  poor  soil, 
we  should  not  expect  results  so  striking,  as  regards  quan- 
tity of  dissolved  matters,  but  doubtless  they  would  be 
similar  in  kind. 

This  is  shown  by  the  investigations  that  follow. 

Ulbricht  gives  (  Ys.  jSl,  Y.,  207)  the  results  of  the  simi- 
lar treatment  of  four  soils.  1,000  grams  of  each  were 
put  in  contact  with  four  times  as  much  pure  water  for 
three  days,  then  two-thirds  of  the  solution  was  poured  off 
for  analysis,  and  replaced  by  as  much  pure  water;  this 
was  repeated  ten  times.  Partial  analyses  were  made  of 
some  of  the  extracts  thus  obtained ;  we  subjoin  the  pub- 
lished results : 


Dissolved  hy  40,000,000  parts  of  water  from  1,000,000  parts  of- 
Loamy  Sand  from  Heinsdorf. 


1st 
Extract. 

2d 
Extract. 

3d 
Extract. 

4th 
Extract. 

7th 
Extract. 

10th 
Extract. 

Potash  ... 

SOX 

95 

30>^ 
trace. 

15 
14 
39 
12 

IK 

15 

21 

38 

10 

3 

8     !      ■ 

4 

Soda.   .. 

18 

39 

10 

3 

11 

Lime 

Magnesia 

Phosphoric  acid... 

Total 

190 

81K 

87 

78 

AQUEOUS    SOLUTION"    OP   THE    SOIL. 


325 


Loamy  Sand  from  TValilsdorf. 


Potash , 

Soda. 

Lime 

Magnesia , 

Phosphoric  acid. 


23 

12 

13 

6 

26 

16 

20 

16 

116 

43 

39 

42 

48 

36X 

15 

14 

12 

14 

7 

3 

4 

4 

208K 

89 

90 

80 

Total . 


Loamy  ferruginous  Sand  from  Dahme,  containing  4^^ 
of  humus. 


Potash 

7 
41 
96 
14 

trace. 

6 
11 
70 
]0 

2 

7 
26 
55 

9 
trace. 

7 

17 

48 

7 

1 

62 
8 

3 

Soda 

8 

Lime 

Magnesia. 

Phosphoric  acid.. 

Total 

158 

99 

97 

80 

Fine  Sandy  Loam  from  Palkenberg. 


Potash 

Soda 

Lime 

Magnesia 

Phosphoric  acid. 


15 

11 

9 

9 

47 

12 

12 

8 

47 

27 

19 

18 

17 

8 

5 

6 

3 

2 

trace. 

trace. 

129 

60 

45 

41 

Total. 


As  Schulze  remarks,  it  is  practically  impossible  to  ex- 
haust a  soil  completely  by  water.  This  liquid  will  still 
dissolve  something  after  the  most  prolonged  or  frequently 
renewed  action,  as  not  one  of  the  components  of  the  soil 
is  possessed  of  absolute  insolubility,  although  in  a  sterile 
soil  the  amount  of  matters  taken  up  would  presently  be- 
c6me  what  the  chemist  terms  "  traces,"  or  might  be  such 
at  the  outset. 

The  two  analyses  by  Krocker,  a  and  5,  p.  314,  made 
on  water  from  the  same  drain,  gathered  at  an  interval  of 
one  month,  further  show  that  water,  rapidly  percolating 
the  soil,  continuously  finds  and  takes  up  new  portions  of 
all  its  ingredients. 

In  addition  to  the  simple  solution  of  matters,  the  soil 
suffers  constantly  the  chemical  changes  which  have  been 
already  noticed,  and  are  expressed  by  the  term  weather- 


326  HOW    CEOPS    FEED. 

ing.  Matters  insoluble  in  water  to-day  become  soluble 
to-morrow,  and  substances  that  to-morrow  resist  the  action 
of  water  are  taken  up  the  day  after.  In  this  way  there 
is  no  limit  to  the  solution  of  the  soil,  and  we  cannot  there- 
fore infer  from  what  the  soil  yields  to  water  at  any  given 
moment  nor  from  what  is  taken  out  of  it  by  any  given 
amount  of  water,  the  real  extent  to  which  aqueous  action 
operates,  during  the  long  period  of  vegetable  growth,  to 
present  to  the  roots  of  a  crop  the  indispensable  ingredi- 
ents of  its  food. 

The  discussion  of  the  question  as  to  the  capacity  of 
water  to  dissolve  from  the  soil  enough  of  the  various  in- 
gredients to  feed  crops,  while  satisfactorily  establishing 
this  capacity  in  case  of  rich  soils,  and"  making  evident 
that  in  poor  soils  most  of  the  inorganic  matters  are  pre- 
sented to  vegetation  by  water  in  sufficient  quantity,  does 
not  entirely  satisfy  us  in  reference  to  some  of  the  needful 
elements  of  the  plant,  especially  phosphoric  acid. 

It  is  therefore  appropriate,  in  this  place,  to  pursue  fur- 
ther inquiries  into  the  mode  by  which  vegetation  acquires 
food  from  the  soil,  although  to  do  so  will  somewhat  inter- 
rupt the  general  plan  of  our  chapter. 

Direct  action  of  Hoots  upon  tlie  Soil. — In  noticing 
the  means  by  which  rocks  are  converted  into  soils,  the 
action  of  the  organic  acids  of  the  living  plant  has  been 
mentioned.  Since  that  chapter  was  written,  further  evi- 
dence has  been  obtained  concerning  the  influence  of  the 
plant  on  the  soil,  which  we  now  proceed  to  adduce. 

Sachs  {Experimental  Physiologie^  189)  gives  an  ac- 
count of  observations  made  by  him  on  the  action  of  roots 
on  marble,  dolomite  (carbonate  of  lime  and  magnesia), 
magnesite  (carbonate  of  magnesia),  osteolite  (phosphate 
of  lime),  gypsum,  and  glass.  Polished  plates  of  these 
substances  were  j)laced  at  the  bottom  of  suitable  vessels 
and  covered  several  inches  in  depth  with  fine  quartz  sand. 
Seeds  of  various  plants  were  planted  in  the  sand  and  kepi 


DIRECT   ACTION    OF   HOOTS    UPOX   THE    SOIL.  327 

moist.  The  roots  penetrated  the  sand  and  came  in  con- 
tact with  the  plates  below,  and  branched  horizontally  on 
their  surfaces.  After  several  days  or  weeks  the  plates 
were  removed  and  examined.  The  plants  employed  were 
the  bean,  maize,  squash,  and  wheat.  The  carbonates  of 
lime  and  magnesia  and  the  phosphate  of  lime  were  plain- 
ly corroded  where  they  had  been  in  contact  with  the 
roots,  so  that  the  course  of  the  latter  could  be  traced  with- 
out difficulty.  Even  the  action  of  the  root-hairs  was  mani- 
fest as  a  faint  roughening  of  the  surface  of  the  stone 
either  side  of  the  path  of  the  root.  Gypsum  and  glass 
were  not  perceptibly  acted  on. 

Dietrich  has  made  a  series  of  experiments  {Soffmann^ 
tTahreshericht,  YI,  3)  on  the  amount  of  matters  made  solu- 
ble from  basalt  and  sandstone,  both  coarsely  powdered, 
and  kept  watered  with  equal  quantities  of  distilled  water, 
when  supporting  and  when  free  from  vegetation.  The 
crushed  rocks  were  employed  in  quantities  of  9  and  11 
lbs. ;  they  were  well  washed  before  the  trials  with  dis- 
tilled water,  and  access  of  dust  was  prevented  by  a  layer 
of  cotton  batting  upon  the  surface.  After  removing  the 
plants,  at  the  termination  of  the  experiments,  each  sam- 
ple of  rock-soil  was  washed  with  the  same  quantity  of 
water,  to  which  a  hundredth  of  nitric  acid  had  been 
added.  It  was  found  that  the  plants  employed,  especially 
lupins,  peas,  vetches,  spurry,  and  buckwheat,  assisted  in 
the  decomposition  and  solution  of  the  basalt  and  sand- 
stone. Not  only  did  these  plants  take  up  mineral  mat- 
ters from  the  rock,  but  the  latter  contained  besides,  a 
larger  amount  of  soluble  matters  than  was  found  in  the 
experiments  where  no  plants  were  made  to  grow.  The 
cereal  grains  had  the  same  effect,  but  in  less  degree.  In 
the  subjoined  table  we  give  the  total  quantities  of  sub- 
stances dissolved  under  the  influence  of  the  growing 
vegetation.  These  figures  were  obtained  by  adding  to 
what  was  found  in  the  washiness  of  the  rock-soils  the  ash 


On  11  lbs. 

of 

basalt. 

0.749  grams. 

0.713      " 

0.365      " 

0.327      " 

0.251      " 

0.196      " 

0.132      " 

328  HOW   CROPS   FEED. 

of  the  crops,  and  subtracting  from  tliat  sum  the  ash  of 
the  seeds,  together  with  the  matters  made  soluble  in  the 
same  soils,  which  had  sustained  no  plants,  but  which  had 
been  treated  otherwise  in  a  similar  manner. 

MATTERS   DISSOLVED  BY  ACTION   OF   ROOTS. 

On  9  lbs.  of 
sandstone. 

Of  3  lupin  plants 0.608  grams. 

"    3  pea  "     0.481      " 

"20spurry      "     0.268      " 

"  10  buckwh't  "     0.232      " 

"4  vetch        "     0.221      " 

"    8  wheat       "     0.027      " 

"    8  rye  "     0.014      " 

These  trials  appear  to  show  conclusively  that  plants 
exert  a  decided  effect  on  the  soil.  We  are  not  informed, 
however,  what  particular  substances  are  rendered  soluble 
under  this  influence. 

We  conclude,  then,  that  the  direct  action  of  the  roots 
of  a  crop  may  in  all  cases  contribute  toward  supplying  it 
with  food,  and  in  many  instances  may  be  absolutely 
essential  to  its  satisfactory  growth. 

Furt&cr  Notice  ©f  Matters  Soluble  la  Water. — The 

analyses  we  have  quoted  show  that  every  chemical  ele- 
ment of  the  soil  may  pass  into  aqueous  solution.  They 
also  show  that  some  substances  are  dissolved  more  easily 
and  in  greater  quantity  than  others. 

In  general,  chlorine^  nitric  acid,  and  sulphuric  acid, 
are  most  readily  and  completely  taken  up  by  water,  and, 
for  the  most  part,  in  combination  with  liwx,  soda,  and, 
magnesia.  In  some  cases,  sulphuric  acid  appears  to  exist 
in  a  difficultly  soluble  condition  ( Van  JBemmelen,  Vs. 
St.,  VIII.,  263). 

Potash,  ammonia,  oxide  of  iron,  alumina,  silica,  and 
phosphoric  acid,  are  the  substances  which  are  usually 
soluble  in  but  small  25i*oportion.     These,  together   with 


ACID    SOLUTION   OF   THE   SOIL.  329 

lime,  magnesia,  and  soda,  it  is  difficult  or  impossible  to 
wash  out  completely  from  a  soil  of  good  quality. 

Very  poor  soils  may  be  deficient  in  soluble  forms  of 
any  or  several  of  tbe  above  ingredients,  and  therefore 
readily  admit  of  nearly  complete  extraction  by  a  small 
amount  of  water. 

Certain  soils  contain  soluble  salts  of  iron  and  alumina 
(sulphates  and  humates)  in  considerable  quantity,  and 
are  for  that  reason  unproductive.  Such  are  many  marsh 
lands,  as  well  as  upland  soils  containing  bisulphide  of  iron 
(iron  pyrites),  of  the  kind  that  readily  oxidizes  to  sulphate 
of  jDrotoxide  of  iron  (copperas). 

§3. 

SOLUTION  OF  THE  SOIL  IN  STRONG  ACIDS. 

The  strong  acids,  hydrochloric  (muriatic),  nitric,  and 
sulphuric,  by  virtue  of  their  vigorous  affinities,  readily 
remove  from  the  soil  a  considerable  quantity  of  all  its 
mineral  ingredients.  The  quantity  thus  taken  up  is 
greatly  more  than  can  be  dissolved  in  water,  and  is,  in 
general,  the  greater,  the  more  fertile  the  soil.  Exceptions 
are  soils  consisting  largely  of  carbonate  of  lime  (chalk 
soils),  or  compounds  of  iron  (ochreous  soils).  The  differ- 
ent acids  above  named  exercise  very  unlike  solvent  effects 
according  to  their  concentration,  the  time  of  their  action, 
the  temperature  at  which  they  are  applied,  and  the  chemi- 
cal nature  and  state  of  division  of  the  soil. 

The  deportment  of  the  minerals  which  chiefly  constitute 
the  soil  towards  these  acids  will  enable  us  to  under- 
stand their  action  upon  the  soil  itself.  Of  these  minerals 
quartz,  feldspar,  mica,  hornblende,  augite,  talc,  steatite, 
kaolinite,  chrysolite,  and  chlorite,  when  not  altered  by 
weathering,  nearly  or  altogether  resist  the  action  of  even 
hot  and  moderately  strong  hydrochloric  and  nitric  acids. 


330  HOW    CROPS    FEED. 

On  the  other  hand,  all  carbonates,  sulphates,  and  phos- 
phates, are  completely  dissolved,  while  the  zeolites  and 
serpentine  are  decomposed,  their  alkalies,  lime,  etc.,  enter- 
ing into  solution,  and  the  silica  they  contain  separating,  for 
the  most  part,  as  gelatinous  hydrate. 

According  to  the  nature  of  the  soil,  and  the  concentra- 
tion of  the  reagent,  hydrochloric  acid,  the  solvent  usually 
employed,  takes  up  from  two  to  fifteen  or  more  per  cent. 

Very  dilute  acids  remove  from  the  soil  the  bases,  lime, 
magnesia,  potash,  and  soda,  in  scarcely  greater  quantity 
than  they  are  united  with  chlorine,  and  with  sulphuric, 
phosphoric,  carbonic,  and  nitric  acids.  Treatment  with 
stronger  acids  takes  up  the  bases  above  mentioned,  par- 
ticularly lime  and  magnesia,  in  greater  proportion  than 
the  acids  specified.  We  find  that,  by  the  stronger  acids, 
silica  is  displaced  from  combination  (and  may  be  taken 
up  by  boiling  the  soil  with  solution  of  soda  after  treat- 
ment with  the  acid).  It  hence  follows  that  silicates,  such 
as  are  decomposable  by  acids,  (zeolites)  exist  in  the  soil, 
although  we  cannot  recognize  them  directly  by  inspec- 
tion even  with  the  help  of  the  microscope.  To  this  point 
we  shall  subsequently  recur. 

§  4. 
PORTION  OF   SOIL  INSOLUBLE  IN   ACIDS. 

"When  a  soil  has  been  boiled  with  concentrated  hydro- 
chloric acid  for  some  time,  or  until  this  solvent  exerts  no 
further  action,  there  may  remain  quartz,  feldspar,  mica, 
hornblende,  augite,  and  kaolinite  (clay),  together  with 
other  similar  silicates,  which,  in  many  cases,  are  ingredients 
of  the  soil.  Treatment  with  concentrated  sulphuric  acid 
at  very  high  temperatures  (Mitscherlich),  or  syrupy  phos- 
phoric acid  (A.  Miiller),  decomposes  all  these  minerals, 
quartz  alone  excepted.     By  making,  therefore,  in  the  first 


CHEMICAL    ACTION    IN    THE    SOIL.  831 

place,  a  mechanical  analysis,  as  described  on  page  147,  and 
subjecting  the  fine  portion,  which  consists  entirely  or  in 
great  part  of  clay,  to  the  action  of  these  acids,  the  quan- 
tity of  clay  may  be  approximately  estimated.  Or,  by 
melting  the  portion  insoluble  in  acids  with  carbonate  of 
soda,  or  acting  upon  it  with  hydrofluoric  acid,  the  whole 
may  be  decomposed,  and  its  elementary  composition  be 
ascertained  by  further  analysis. 

Notwithstanding  an  immense  amount  of  labor  has  been 
expended  in  studying  the  composition  of  soils,  and  chiefly 
in  ascertaining  what  and  how  much,  acids  dissolve  from 
them,  we  have,  unfortunately,  very  few  results  in  the  way 
of  general  principles  that  are  of  application,  either  to  a 
scientific  or  a  practical  purpose.  In  a  number  of  special 
cases,  however,  these  investigations  have  proved  exceed- 
ingly instructive  and  useful. 

§5. 

REACTIONS  BY  WHICH  THE  SOLUBILITY  OF  THE  ELEMENTS 
OF   THE   SOIL    IS    ALTERED.      SOLVENT    EFFECT    OF 
VARIOUS    SUBSTANCES    THAT   ARE    COMMONLY 
BROUGHT    TO    ACT    UPON   SOILS.      THE  AB- 
SORPTIVE AND  FIXING  POWER  OF  SOILS. 

Chemical  Action  in  the  Soil, — Chemistry  has  proved 
that  the  soil  is  by  no  means  the  inert  thing  it  appears  to 
be.  It  is  not  a  passive  jumble  of  rock-dust,  out  of  which 
air  and  water  extract  the  food  of  vegetation.  It  is  not 
simply  a  stage  on  which  the  plant  performs  the  drama  of 
growth.  It  is,  on  the  contrary,  in  itself,  the  theater  of 
ceaseless  activities ;  the  seat  of  perpetual  and  complicated 
changes. 

A  large  share  of  the  rocks  now  accessible  to  our  study 
at  the  earth's  surface  have  once  been  soil,  or  in  the  condi- 
tion of  soil.  "Not  only  the  immense  masses  of  stratified 
limestones,  sandstones,  slates,  and  shales,  that  cover  so 


332  HOW    CROPS   FEED. 

large  a  part  of  the  Middle  States,  but  most  of  the  rocks 
of  N'ew  England  have  been  soil,  and  have  su^^ported  vege- 
table and  animal  life,  as  is  proved  by  the  fossil  relics  that 
have  been  disinterred  from  them. 

"We  have  explained  the  agencies,  mechanical  and  chemi- 
cal, by  which  our  soils  have  been  formed  and  are  forming 
from  the  rocks.  By  a  reverse  metamorphosis,  involving 
also  the  cooperation  of  mechanical  and  chemical  and  even 
of  vital  influences,  the  soils  of  earher  ages  have  been  so- 
lidified and  cemented  to  our  rocks.  ISlov,  indeed,  is  this 
process  of  rock-making  brought  to  a  conclusion.  It  is 
going  on  at  the  present  day  on  a  stupendous  scale  in  vari- 
ous parts  of  the  world,  as  the  observations  of  geologists 
abundantly  demonstrate.  If  we  moisten  sand  with  a  so- 
lution of  silicate  of  soda  or  silicate  of  potash,  and  then 
drench  it  with  chloride  of  calcium,  it  shortly  hardens  to 
a  rock-like  mass,  possessing  enough  firmness  to  answer 
many  building  purposes  (Ransome's  artificial  stone).  A 
mixture  of  lime,  sand,  and  water,  slowly  acquires  a  simi- 
lar hardness.  Many  clay-limestones  yield,  on  calcination, 
a  material  (water-lime  cement)  which  hardens  speedily, 
even  under  water,  and  becomes,  to  all  intents,  a  rock. 
Analogous  changes  proceed  in  the  soil  itself.  Hard  pan, 
which  forms  at  the  plow-sole  in  cultivated  fields,  and 
moor-bed  pan,  which  makes  a  peat  basin  impervious  to 
water  in  beds  of  sand  and  gravel,  are  of  the  same  nature. 

The  bonds  which  hold  together  the  elements  of  feldspar, 
of  mica,  of  a  zeolite,  or  of  slate,  may  be  indeed  loosened 
and  overcome  by  a  superior  force,  but  they  are  not  de- 
stroyed, and  reassert  their  power  when  the  proper  cir- 
cumstances concur.  The  disintegration  of  rock  into  soil 
is,  for  the  most  part,  a  slow  and  unnoticed  change.  So, 
too,  is  the  reversion  of  soil  to  rock,  but  it  nevertheless 
goes  on.  The  cultivable  surface  of  the  earth  is,  however, 
on  the  whole,  far  more  favorable  to  disintegration  than 
to  petrifaction.     Nevertheless,  the  chemical  affinities  and 


ABSORPTIVE   POWEK   OF   THE    SOIL.  333 

physical  qualities  tbat  oppose  disintegration  are  inherent 
in  the  soil,  and  constantly  manifest  themselves  in  the 
kind,  if  not  in  the  degree,  involved  in  the  making  of  rocks. 
The  fourteen  elementary  substances  that  exist  in  all  soils 
are  capable  of  forming  and  tend  to  form  a  multitude  of 
combinations.  In  our  enumeration  of  the  minerals  from 
which  soils  originate,  we  have  instanced  but  a  few,  the 
more  common  of  the  many  which  may,  in  fact,  contribute 
to  its  formation.  The  mineralogist  counts  by  hundreds 
the  natural  compounds  of  these  very  elements,  com- 
pounds which,  from  their  capability  of  crystallization, 
occur  in  a  visibly  distinguishable  shape.  The  chemist  is 
able,  by  putting  together  these  elements  in  different  pro- 
portions, and  under  various  circumstances,  to  identify  a 
further  number  of  their  compounds,  and  both  mineralogy 
and  chemistry  daily  attest  the  discovery  of  new  combi- 
nations of  these  same  elements  of  the  soil. 

We  cannot  examine  the  soil  directly  for  many  of  the 
substances  which  most  certainly  exist  in  it,  on  account  of 
their  being  indistinguishable  to  the  eye  or  other  senses, 
even  when  assisted  by  the  best  instruments  of  vision. 
We  have  learned  to  infer  their  existence  either  from  analo- 
gies with  what  is  visibly  revealed  in  other  spheres  of  ob- 
servation, or  from  the  changes  we  are  able  to  bring  about 
and  measure  by  the  art  of  chemical  analysis. 

Absorptiye  Power  of  the  Soil. — We  have  already 
drawn  attention  to  the  fact  that  various  substances,  when 
put  in  contact  with  the  soil,  in  a  state  of  solution  in  water, 
are  withdrawn  from  the  liquid  and  held  by  the  soil.  As 
has  been  mentioned  on  p.  175,  the  first  appreciative  rec- 
ord of  this  fact  appears  to  have  been  published  by 
Bronner,  in  1836.  In  bis  work  on  Grape  Culture  occur 
the  following  passages  :  "  Fill  a  bottle  which  has  a  small 
hole  in  its  bottom  with  fine  river  sand  or  half-dry  sifted 
garden  earth.  Pour  gradually  into  the  bottle  thick  and 
putrefied  dung-liquor  until  its  contents  are  saturated.  The 


334  HOAV    CEOPS    FEED. 

liquid  that  flows  out  at  tiie  lower  opening  appears  almost 
odorless  and  colorless,  and  has  entirely  lost  its  original 
properties."  After  instancing  the  facts  that  wells  situ- 
ated near  dung-pits  are  not  spoiled  by  the  latter,  and  that 
the  foul  water  of  the  Seine  at  Paris  becomes  potable  af- 
ter filtering  through  porous  sandstone,  Bronner  contin- 
ues: "These  examples  sufficiently  prove  that  the  soil, 
even  sand,  possesses  the  property  of  attracting  and  fully 
absorbing  the  extractive  matters  so  that  the  boater  which 
subsequently  passes  is  not  ahle  to  remove  theyn  ^  even  the 
soluble  salts  are  absorbed,  and  are  only  washed  out  to  a 
small  extent  by  7iew  quantities  of  water J^ 

It  was  subsequently  observed  in  the  laboratory  of 
Liebig,  at  Giessen,  that  water  holdiag  ammonia  in  solu- 
tion, when  poured  upon  clay,  ran  through  deprived  of 
this  substance.  Afterward,  Messrs.  Thompson  and  Hux- 
table,  of  England,  repeated  and  extended  the  observa- 
tions of  Bronner,  and  in  1850,  Professor  Way,  then 
chemist  to  the  Roy.  Ag.  Soc.  of  Eng.,  published  in  the 
Journal  of  that  Society,  Vol.  XL,  pp.  313-379  an  account 
of  a  most  laborious  and  fruitful  investigation  of  the  sub- 
ject. Since  that  time  many  chemists  have  studied  the 
phenomena  of  absorption,  and  the  results  of  these  labors 
will  be  briefly  stated  in  the  paragraphs  that  follow. 

There  are  two  kinds  of  absorptive  power  exhibited  by 
soils.  One  is  purely  physical,  and  is  the  consequence  of 
adhesion  or  surface-attraction,  exerted  by  the  particles  of 
certain  ingredients  of  the  soil.  The  other  is  a  chemical 
action,  and  results  from  a  play  of  affinities  among  certain 
of  its  components. 

The  physical  absorptive  power  of  various  bodies,  in- 
cluding the  soil,  has  been  already  noticed  in  some  detail 
(pp.  161-176).  In  experiments  like  those  of  Bronner, 
just  alluded  to,  the  absorption  of  the  coloring  and  odor- 
ous ingredients  of  dung-liquor  is  doubtless  a  physical 
process.    These  substances  are  separated  from  solution  by 


ABSOEPTIVE   POWEE    OF   THE    SOIL.  335 

the  soil  just  as  a  mass  of  clean  wool  separates  indigo  from 
the  liquor  of  a  dye-vat,  or  as  bone-charcoal  removes  the 
brown  color  from  syrup. 

Chemical  absorptions  depend  upon  the  formation  of 
new  compounds,  and  in  many  cases  occasion  chemical 
decompositions  and  displacements  in  such  a  manner  that 
while  one  ingredient  is  absorbed,  and  becomes  in  a  sense 
fixed,  another  is  released  from  combination  and  becomes 
soluble.  Brief  notice  has  already  been  made  of  the 
chemical  absorption  of  ammonia  by  the  soil  (p.  243). 
We  shall  now  enter  upon  a  fuller  discussion  of  this  and 
allied  phenomena. 

When  solutions  of  the  various  soluble  acids  and  bases 
existing  in  the  soil,  or  of  their  salts,  are  i^ut  in  contact 
with  any  ordinary  earth  for  a  short  time,  suitable  exami- 
nation proves  that  in  most  cases  a  chemical  change  takes 
place, — a  reaction  occurs  between  the  soil  and  the 
substance. 

If  we  provide  a  number  of  tall,  narrow  lamp-chimneys 
or  similar  tubes  of  glass,  place  on  the  flanged  end  of  each 
a  disk  of  cotton-batting,  tying  over  it  a  piece  of  muslin, 
then  support  them  vertically  in  clamps  or  by  strings,  and 
fill  each  of  them  compactly,  two-thirds  full  of  ordinary 
loamy  soil,  which  should  be  free  from  lumps,  we  have  an 
arrangement  suitable  for  the  study  of  the  absorptive 
power  in  question. 

Let  now  solutions,  containing  various  soluble  salts 
of  the  acids  and  bases  existing  in  the  soil,  be  pre- 
pared. These  solutions  should  be  quite  dilute,  but 
still  admit  of  ready  identification  by  their  taste  or  by 
simple  tests.  We  may  employ,  for  example,  any  or  all  of 
the  following  compounds,  viz.,  saltpeter,  common  salt,  sul- 
phate of  magnesia,  phosphate  of  soda,  and  silicate  of  soda. 

If  we  pour  solution  of  saltpeter  on  the  soil,  which 
should  admit  of  its  ready  but  not  too  rapid  percolation, 
we  shall  find  that  the  first  portions  of  liquid  which  pass 


836  HOW    CEOPS    FEED. 

are  no  longer  a  solution  of  nitrate  of  potash,  but  one  of 
nitrates  of  lime,  magnesia,  and  soda.  The  potash  has 
disappeared  from  solution*  and  become  a  constituent  of 
the  soil,  while  other  bases,  chiefly  lime,  have  been  dis- 
placed from  the  soil,  and  now  exist  in  the  solution  with 
the  nitric  acid. 

If  we  operate  in  a  similar  manner  on  a  fresh  tube 
of  soil  with  solution  of  salt  (chloride  of  sodium),  we 
shall  find  by  chemical  examination  that  the  soda  of  the 
salt  is  absorbed  by  the  soil,  while  the  chlorine  passes 
through  in  combination  with  lime,  magnesia,  and  potash. 
In  case  of  sulphate  of  magnesia,  magnesia  is  retained,  and 
sulphates  of  lime,  etc.,  pass  through.  With  phosphates 
and  silicates  we  find  that  not  only  the  base,  but  also  these 
acids  are  retained. 

Law  of  Absorption  and  ©Isplacemeiit. — From  a  great 
number  of  experiments  made  by  Way,  Liebig,  Brustlein, 
Henneberg  and  Stohmann,  Rautenberg,  Peters,  Weinhold, 
KilUenberg,  Heiden,  Knop,  and  others,  it  is  established 
as  a  general  fact  that  all  cultivable  soils  arc  able  to  de- 
compose salts  of  the  alkalies  and  alkali  earths  in  a  state 
of  solution,  in  such  a  manner  as  to  retain  the  base  together 
with  phosphoric  and  silicic  acids,  while  chlorine,  nitric 
acid,  and  sulphuric  acid,  remained  dissolved,  in  union  with 
some  other  base  or  bases  besides  the  one  with  which  they 
were  originally  combined.  The  absorptive  power  of  the 
soil  is,  however,  limited.  After  it  has  removed  a  certain 
quantity  of  potash,  etc.,  from  solution  its  action  ceases,  it 
has  become  saturated,  and  can  take  up  no  more.  If, 
therefore,  a  large  bulk  of  solution  be  filtered  through  a 
small  volume  of  earth,  the  liquid,  after  a  time,  passes 
throuorh  unaltered. 


*  The  absence  of  potash  may  be  shown  by  aid  of  strong,  cold  solution  of 
tartaric  acid^  which  will  precipitate  bitartrate  of  potash  (cream  of  tartar)  from 
the  original  solution,  if  not  too  dilute,  but  not  from  that  which  has  filtered 
through  the  soil.  The  presence  of  lime  in  the  liquid  that  passes  the  soil  may  be 
shown  by  adding  to  it  either  carbonate  or  oxalate  of  ammonia, 


ABSOEPTIVE    POWER    OP   THE    SOIL.  337 

Experiments  to  ascertain  liow  much  of  a  substance  the  soil  is  able  to 
absorb  are  made  by  putting  a  known  amount  of  the  dnj  soil  (e.  g.  100 
grms.)  in  a  bottle  with  a  given  volume  (e.  g.  500  cubic  cent.)  of  solution 
whose  content  of  substance  has  been  accurately  determined.  The  solu- 
tions are  most  conveniently  jorepared  so  as  to  contain  as  many  grms.  of 
the  salt  to  the  liter  of  water  as  corresponds  to  the  atomic  weight  or 
equivalent  of  the  former,  or  one-half,  one-tenth,  etc.,  of  that  amount. 
The  soil  and  solution  are  kept  in  contact  with  occasional  agitation  for 
some  hours  or  days,  and  then  a  measured  portion  of  the  liquid  is 
filtered  off  and  subjected  to  chemical  analysis. 

The  absorptive  power  of  the  soil  is  exerted  unequally 
towards  mdividual  substances.  Thus,  in  Peters'  ex23eri- 
ments  ( Vs.  St.,  11. ,  140),  the  soil  he  operated  with  absorb- 
ed the  bases  in  quantities  diminishing  in  the  following 
order : 

Potash,  Ammonia,  Soda,  Magnesia,  Lime. 

Another    soil,    experimented    upon     by    Kiillenberg 
(Jahresbericht  uber  Agricidtur.  Chemie,  1865,  p.  15),  ab- 
sorbed in  a  different  order  of  quantity,  as  follows : 
Ammonia,  Potash,  Magnesia,  Lime,  Soda. 

As  might  be  expected,  different  soils  exert  absorptive 
power  tovmrds  the  same  substance  to  an  unequal  extent. 
Rautenberg  {Senneberg^s  Jour,  fur  Landwirtliscliaft, 
1862,  p.  62),  operated  with  nine  soils,  10,000  parts  of  which, 
under  ]3recisely  similar  circumstances,  absorbed  quantities 
of  ammonia  ranging  from  7  to  25  parts. 

The  time  required  for  absorption  is  usually  short. 
Way  found  that  in  most  cases  the  absorption  of  ammonia 
was  complete  in  half  an  hour.  Peters,  however,  observed 
that  48  hours  were  requisite  for  the  saturation  of  the  soil 
he  employed  with  potash,  and  in  the  experiments  of  Hen- 
neberg  and  Stohmann  {Senneberg^s  Journal.,  1859,  p.  35), 
phosphoric  acid  continued  to  be  fixed  after  the  expiration 
of  24  hours. 

The  strength  of  the  solution  influences  the  extent  of 
absorption.     The  stronger  the  solution,  the  more  substance 
is  taken  up  from  it  by  the  soil.     Thus,  in  Peters'  experi- 
15 


338  HOW    CROPS    FEED. 

ments,  100  grms.  of  soil  absorbed  from  250  cubic  centi- 
meters of  solutions  of  cliloride  of  potassium  of  various 
degrees  of  concentration,  as  follows : 

strength  of  Solution.  Potash  absorbed  by 

Designa-     Quantity  of  potash  m  250  c.c.  100  parts  By  10,000  parts  in  Proportion 

tion.                      of  solution.  of  soil.      round  numbers.  absorbed. 

"Loeqniv.  =            0.1472  gram.  0. '9888  gram.            10  2|^ 

ho       "  =             0.2944  "  0.1381      '•                14  i|2 

loo       "  =:             0.5888  "  0.1990      "                20  Ms 

ho       "  =             l.-^Ta  "  0.3124      "                31  i|4 

I5        "  =             2.3555  "  0.4503      "                45  Ma 

A  glance  at  tlie  rigbt-liand  column  sbows  that  although 
ahsohitely  less  potash  is  absorbed  from  a  weak  solution 
than  from  a  strong  one,  yet  the  weak  solutions  yield 
relatively  more  than  those  which  are  concentrated. 

The  quantity  of  base  absorbed  in  a  given  time,  also  de- 
pends upon  the  relative  mass  of  the  solution  and  soil.  In 
these  experiments  Peters  treated  a  soil  with  various  bulks 
of  ^  l^n  solution  of  chloride  of  potassium.  The  results  are 
subjoined : — 

From     250  c.c.  of  solution  10,000  parts  of  soil  absorbed  20  parts. 
500    "     "        "  "  "      "      "  "        25      " 

"      1,000    "     "        "  "         "      "      "  "        29     " 

The  quantity  of  a  substance  absorbed  by  the  soil  de- 
pends somewhat  on  the  state  of  combination  it  is  in,  i.  e., 
on  the  substances  with  which  it  is  associated.  Peters 
found,  for  example,  that  10,000  parts  of  soil  absorbed  from 
solutions  of  a  number  of  potash-salts,  each  containing 
^1 23  of  an  equivalent  of  that  base  expressed  in  grams,  to 
the  liter,  the  following  quantities  of  potash : — 
From  phosphate,  49  parts, 

hydrate,  40      " 

carbonate,  32      " 

bicarbonate,  28      " 

nitrate,  25      " 

sulphate,  21      " 

chloride*  and  carbonate,  21      " 
chloride,  20      " 


*  Chloride  of  Potassium,  KC! 


ABSOEPTIVE    POWEE    OP   THE    SOIL.  dW 

We  observe  that  potash  was  absorbed  in  this  case  in 
largest  proportion  from  the  phosphate,  and  in  least  from 
the  chloride.  Henneberg  and  Stohmann,  operating  on  a 
garden  soil,  observed  a  somewhat  different  deportment  of 
it  towards  ammonia-salts.  10,000  parts  of  soil  absorbed 
as  follows : — 


From  phosphate,  21      parts. 

"     hydrate,  13  " 

"     sulphate,  12    '      " 

"     hydrate  and  chloride,*  11^  I2      " 
"     chloride,  11 

"     nitrate,  11  " 

Fixation  neither  complete  nor  permanent. — A  point 
of  the  utmost  importance  is  that  none  of  the  bases  are 
ever  completely/  absorbed  even  from  the  most  dilute  solu- 
tions. Liebig  indeed,  formerly  believed  that  potash  is  en- 
tirely removed  from  its  solutions.  We  find,  in  fact,  that 
when  a  dilute  solution  of  potash  is  slowly  filtered  through 
a  large  body  of  soil,  the  first  portions  contain  so  little  of 
this  substance  as  to  give  no  indication  to  the  usual  tests. 
These  portions  are  similar  in  composition  to  drain-waters, 
and  like  the  latter  they  contain  potash  in  very  minute 
though  appreciable  quantity. 

In  accordance  with  the  above  fact,  it  is  found  that  water 
will  dissolve  and  remove  a  portion  of  the  potash,  etc., 
which  a  soil  has  absorbed. 

Peters  ])laced  in  250  c.c.  of  a  solution  of  chloride  of 
potassium  100  grams  of  soil,  which  absorbed  0.2114  gram 
of  potash.  At  the  expiration  of  two  days,  one-half  of  the 
solution  was  removed,  and  its  place  was  supplied  with 
pure  water.  After  two  days  more,  one-half  of  the  liquid 
was  again  removed,  and  an  equal  volume  of  water  added  * 


Chloride  of  Ammoninm,  ]Sr[T4Cl. 


340 


HOW    CROPS   FEED. 


and  this  process  was  repeated  ten  times, 
thus  in  the  several  washing^s  as  follows : 


The  soil  lost 


In  2d, 
0.0075 


3d, 
0.0096 


4th, 
0.0082 
In  8th, 
0.0112 


5th, 
0.0069 

9th, 
0.0201 


6th,  7th    exti'act. 

0.0075  0.0082  grams. 

10th    extract. 
0.0S3  fframs. 


Eemoved  in  all,    0.0875  gram  of  potash. 
Kemainedin  soil,  0.1239  gram. 


In  these  experiments  one  part  of  absorbed  potash  re- 
quired 28,100  parts  of  water  for  solution. 

Similar  results  were  obtained  by  Ilenneberg  and  Stoh- 
mann  with  a  soil  which  had  absorbed  ammonia ;  one  part 
of  this  base  required  10,000  parts  of  water  for  re-solution. 

It  has  been  already  stated,  that  the  absorption  of  one 
base  is  accompanied  by  the  liberation  of  a  corresponding 
quantity  of  other  bases,  while  the  acid  element,  if  it  be 
sulphuric  or  nitric  acid,  or  chlori7ie,  is  found  in  its 
original  quantity  in  the  solution.  As  an  illustration  of 
this  rule,  the  following  data  obtained  by  Weinhold  in  the 
treatment  of  a  soil  with  sulphate  of  ammonia  are  ad- 
duced. The  quantities  are  expressed  in  grams,  except 
where  otherwise  stated. 

Content  of  Solution 


hefore 

1 

Gf/er 

contact  with  the  soil.        \ 

contact  tvith  the  soil. 

^-- 

^ 

•S 

•^ 

d 

^1 

-^1 

ii 

0 

If 

^1 

1 
1 

1 

1 

1 

1 

300 

0.303 

0.129 

1     0.329 

0.056 

0.012 

0.121 

0.110 

0.049 

IV2 

200 

0.455 

0.193 

1     0.488 

0.120 

0.011 

0.034 

0.105 

0.030 

We  observe  that  the  soil  not  only  retained  no  sulphuric 
acid,  but  gave  up  a  small  quantity  to  the  solution.  Of 
the  ammonia  a  little  more  than  one-half  in  one  case,  and 
three-eighths  in  the  other,  was  absorbed,  and  in  the  solu- 
tion its  place  was  supplied  chiefly  by  lime,  but  to  some 
extent  also  by  potash,  soda,  and  magnesia,  which  were 
dissolved  from  the  soil.  It  is  also  to  be  noticed  that  in 
the  two  cases — unlike  quantities   of   the  same   soil    and 


ABSOEPTIYE    POWEE    OF   THE    SOIL. 


341 


solution  having  been  employed — the  bases  were  displacec^ 
in  quantities  that  bear  to  each  other  no  obvious  relation. 

Another  fact  whicb  follows  from  the  rule  just  illustra- 
ted, is  the  following :  Any  base  that  has  been  absorbed  by 
the  soil,  may  be  released  from  combination  partly  or  en- 
tirely by  any  other. 

Peters  subjected  a  soil  which  had  been  saturated  with 
potash  and  subsequently  washed  copiously  with  water  to 
the  action  of  various  solutions.  The  results,  which  exhib- 
it the  principle  just  stated,  are  subjoined.  The  soil  was 
employed  in  portions  of  100  grams,  each  of  which  con- 
tained 0.204  gram  of  absorbed  potash.  These  were  di- 
gested for  three  days  with  250  c.c.  of  solutions  (of  ni- 
trates) of  the  content  below  indicated. 

For  sake  of  comparison  the  amount  of  matters  taken  up 
by  distilled  water  is  added. 


Dissolved  by  the  solution. 

Content  of 
solution. 

Lime. 

Magne- 
sia. 

Potash. 

Soda. 

Ammo- 
nia. 

Absorbed 
bij  the  soU. 

gram. 
0.2808  soda. 
0.2165  ammonia. 
0.2996  lime. 
0  2317  magnesia. 
Dist.  water. 

0.0671(?) 
0.0322 
0.2380 
0.0542 
trace 

0.0006 

0.0020 
0.1726 

0.0983 
0.1455 
0.1252 
0.1224 
0.0434 

0.2197 
0.0024 
0.0252 
0.0245 
0.0004 

0.1596 

0.0611  soda. 
0.0569  ammonia, 
0.0616  lime. 
0.0591  magnesia. 

We  notice  that  while  distilled  water  dissolved  about  ^  |^ 
of  the  absorbed  potash,  the  saline  solutions  took  up  two, 
three,  or  more  times  that  quantity.  We  observe  further 
that  soda  liberated  lime  and  magnesia,  ammonia  liberated 
lime  and  soda,  lime  brought  into  solution  magnesia  and 
soda,  and  magnesia  set  free  lime  and  soda  from  the  soil 
itself. 

Again,  Way,  Brustlein,  and  Peters,  have  shown  in  case 
of  various  soils  they  experimented  with,  that  the  satura- 
ting of  them  with  one  base  (potash  and  lime  were  tried) 
increases  the  absorbent  poioer  for  other  bases.,  and  on  the 
other  hand.,  treatment  with  acids.,  which  removes  absorbed 
baseSj  diminishes  their  absorptive  power. 


342 


HOW    CROPS   FEED. 


This  fact  is  made  evident  by  tlie  following  data  furnisli- 
ed  by  Peters.     The  soils  employed  were 

:N'o.  1.  Unaltered  Soil. 

ISTo.  2.  Soil  heated  with  hydrochloric  acid  for  some 
time,  then  thoroughly  washed  with  water. 

'No.  3.  No.  2,  boiled  with  10  grams  of  sulphate  of  lime 
and  water,  and  washed. 

No.  4.  No.  2,  boiled  with  solution  of  10  grams  of  chlo- 
ride of  calcium,  and  well  washed  with  water. 

No.  5.  No.  2,  boiled  with  water  and  10  grams  of  car- 
bonate of  lime. 

No.  6.  No.  2,  boiled  with  solution  of  bicarbonate  of 
lime,  and  washed. 

Portions  of  100  grams  of  each  of  the  above  were  placed 
in  contact  with  250  c.c.  of  ^  l^g  solution  of  chloride  of  po- 
tassium for  three  days.     The  results  are  subjoined: 


Number 

Dissolved  by  the  solution. 

Potash  absorbed 

of  soil. 

Lime-. 

Magnesia. 

Soda. 

Chlonne. 

by  the  soil. 

1 

2 

3 

4 

5 

6 

0.0940 
0.0136 
0.0784 
0.0560 
0.1176 
0.1456 

0.0084 

0.0261 
0.0004 
0.0019 
0.0024 
0.0019 

0.4482 
0.4444 
0.4452 
0.4452 
0.4425 
0.4404 

0.1841 
0.0227 
0.0882 
0.1248 
0.1378 
0.2011 

0.0024 
0.0094 
0.0094 
0.0074 

It  is  seen  that  the  soil  which  had  been  washed  with 
acid,  absorbed  but  one-ninth  as  much  as  the  unaltered 
earth.  The  treatment  with  the  various  lime-salts  increas- 
ed the  absorbent  power,  in  the  order  of  the  Table,  until 
in  the  last  instance  it  surpassed  that  of  the  original  soil. 
Here,  too,  we  observe  that  the  absorption  of  potash  ac- 
companies and  is  made  possible  by  the  displacement  of 
other  bases,  (in  this  case  almost  entirely  lime,  since  the 
treatment  with  acid  had  nearly  removed  the  others).  We 
observe  further  that  the  quantity  of  chlorine  remained 
the  same  throughout  (within  the  limits  of  experimental 
error,)  not  being  absorbed  in  any  instance. 

Way  first  showed  that  the  absorptive  power  of  the  soil 


ABSORPTIVE   POWER    OF   THE    SOIL.  343 

is  diminislied  or  even  destroyed  by  burning  or  calcination. 
Peters,  experimenting  on  this  point,  obtained  the  follow- 
ing results : 

Potash  absorbed  from  solution  of  chloride  of  potassium  by 
unburned  burned 

Vegetable  mould,    0.2515  0.0202 

Loam,  0.1841  0.1200 

The  Cause  of  tiae   Absorptive  Power  of  Soils  for 

Bases  when  combined  with  chlorine,  Bulphuric,  and  nitric 
acids,  has  been  the  subject  of  several  extensive  investiga- 
tions. Way,  in  his  papers  already  referred  to,  was  led  to 
conclude  that  tbe  quality  in  question  belongs  to  some  pe- 
culiar compound  or  compounds  that  are  associated  with 
the  clayey  or  impalpable  portion  of  the  soil.  That  these 
bodies  were  compounds  of  the  bases  of  the  soil  with 
silica,  was  a  most  probable  and  legitimate  hypothesis, 
which  he  at  once  sought  to  test  by  experiment. 

Various  natural  silicates,  feldspars,  and  others,  and  some 
artificial  preparations,  were  examined,  but  found  to  be 
destitute  of  action.  Finally,  a  silicate  of  alumina  and 
soda  containing  water  was  prepared,  which  possessed  ab- 
sorptive properties. 

To  produce  this  compound,  pure  alumina  was  dissolved 
in  solution  of  caustic  soda  on  the  one  hand,  and  pure  silica 
in  the  same  solution  on  the  other.  On  mingling  the  two 
liquids,  a  white  precipitate  separated,  which,  when  washed 
from  soluble  matters  and  dried  at  212°,  had  the  following 
composition  * : 

Silica,         46.1 

Alumina,  26.1 

Soda,  15.8 

Water,       12.0 


100.0 


*  Way  gives  the  composition  of  the  anhydrous  salt,  and  says  it  contained, 
dried  at  212°,  about  12  per  cent  of  ivater.  In  the  above  statement  this  w^ater  is  in- 
cluded, since  it  is  obviously  an  essential  ingredient. 


344  HOW    CROPS    FEED. 

This  compound  is  analogous  in  constitution  to  tlie 
zeolites,  in  so  far  as  it  is  a  highly  basic  silicate  containing 
water,  and  is  easy  of  decomposition.  It  is,  in  fact,  de- 
composed by  water  alone,  which  removes  from  it  silicate 
of  soda,  leaving  insoluble  silicate  of  alumina. 

On  digesting  this  soda-silicate  of  alumina  with  a  solu- 
tion of  any  salt  of  lime.  Way  found  that  it  was  decom- 
posed, its  soda  was  eliminated,  and  a  lime-silicate  of 
alumina  was  produced.  In  several  instances  he  succeeded 
in  replacing  nearly  all  the  soda  by  lime.  JPotash-silicate 
of  alumina  was  procured  by  acting  on  either  the  soda  or 
lime  silicate  with  solution  of  a  potash-salt ;  and,  in  a  simi- 
lar manner,  ammonia  and  m^agnesia-silicates  were  gener- 
ated. In  case  of  the  ammonia-compound,  however.  Way 
succeeded  in  replacing  only  about  one-third  of  soda  or 
other  base  by  ammonia.  All  of  these  compounds,  when 
acted  upon  by  pure  water,  yielded  small  proportions  of 
alkali  to  the  latter,  viz. : 

The  soda-       Bilicate  gave  3.36  parts  of  soda        to  10,000  of  water. 
The  potash-         '•         "     2.2T     "     "  potash      "      "        "     " 
The  ammonia-     "■         "     1.06     "     "  ammonia "      "        "     " 

Way  found  furthermore  that  exposure  to  a  strong  heat 
destroyed  the  capacity  of  these  substances  to  undergo  the 
displacements  we  have  mentioned. 

From  these  facts  Way,  concluded  that  there  exist  in  all 
cultivable  soils,  compounds  similar  to  those  he  thus  pro- 
cured artificially,  and  that  it  is  their  presence  which  oc- 
casions the  absorptions  and  displacements  that  have  been 
noticed. 

Way  gives  as  characteristic  of  this  class  of  double  sili- 
cates, that  there  is  a  regular  order  in  which  the  common 
bases  replace  each  other.  He  arranges  them  in  the  fol- 
lowing series : 

Soda — ^Potash — Lime — Magnesia — Ammonia: 
and  according  to  him,  potash  can  replace  soda  but  not  the 
other  bases ;  while  ammonia  replaces  them  all :  or  each  base 


ABSOEPTIVE    POWER    OF    THE    SOIL.  345 

replaces  those  ranged  to  its  left  in  tbe  above  series,  but 
none  of  those  on  its  right.  Way  remarks,  that  "  of  course 
the  reverse  of  tliis  action  cannot  occur."  Liebig  {A7i7i.  der 
Chem.  u.  Pharm.^  xciv,  380)  drew  attention  to  the  fact 
that  Way  himself  in  the  preparation  of  the  potash-alumi- 
na-silicate, demonstrated  that  there  is  no  invariable  order 
of  decomposition.  For,  as  he  asserts,  this  compound  may 
be  obtained  by  digesting  either  the  lime-alumina-silicate,  or 
soda-alumina-silicate  in- nitrate  or  sulphate  of  potash,  when 
the  soda  or  lime  is  dissolved  out  and  replaced  by  potash. 

Way  was  doubtless  led  into  the  mistake  of  assuming  a 
fixed  order  of  replacements  by  considering  these  exchanges 
of  bases  as  regulated  after  the  ordinary  manifestations  of 
chemical  affinity.  His  own  experiments  show  that  among 
these  silicates  there  is  not  only  no  inflexible  order  of  de- 
composition, but  also  no  complete  replacements. 

The  researches  of  Eichhorn,  "  Ueber  die  Einwirkung  ver- 
diinnter  Salzlosungen  auf  Ackererde,"  {Landwirthschaft- 
liches  Centralblatt^  1858,  ii,  169,  and  Pogg.  Ann.^  No.  9, 
1858),  served  to  clear  up  the  discrepancies  of  Way's  in- 
vestigation, and  to  confirm  and  explain  his  facts. 

As  Way's  artificial  silicates  contained  about  12  per  cent 
of  water,  the  happy  thought  occurred  to  Eichhorn  to  test 
the  action  of  saline  solutions  on  the  hydrous  silicates 
(zeolites)  which  occur  in  nature.  He  accordingly  insti- 
tuted some  trials  on  chabazite,  an  abstract  of  which  is 
here  given. 

On  digesting  finely  pulverized  chabazite  (hydrous  sili- 
cate of  alumina  and  lime)  with  dilute  solutions  of  chlo- 
rides of  potassium,  sodium,  ammonium,  lithium,  barium, 
strontium,  calcium,  magnesium,  and  zinc,  sulphate  of 
magnesia,  carbonates  of  soda  and  ammonia,  and  nitrate 
of  cadmium,  he  found  in  every  case  that  the  basic  ele- 
ment of  tbese  salts  became  a  part  of  the  silicate,  while 
Ihne  passed  into  the  solution.  The  rapidity  of  the  re- 
f)lacement  varied  exceedingly.  The  alkali-chlorides  re- 
15* 


346  HOW    CEOPS   FEED. 

acted  evidently  in  two  or  three  days.  Chloride  of  barium 
and  nitrate  of  cadmium  were  slower  in  their  effect.  Chlo- 
rides of  zinc  and  strontium  at  first,  appeared  not  to  react ; 
but  after  twelve  days,  lime  was  found  in  the  solution. 
Chloride  of  magnesium  was  still  tardier  in  replacing  lime. 
Four  grams  of  j)owdered  chabazite  were  digested  with 
4  grams  of  chloride  of  sodium  and  400  cubic  centimeters 
of  water  for  10  days.  The  composition  of  the  original 
mineral  (i,)  and  of  the  same  after  the  action  of  chloride  of  , 
sodium  (ii,)  were  as  follows: 


I. 

II. 

Silica, 

47.44 

48.31 

Alumina, 

20.69 

21.04 

Lime, 

10.87 

6.65 

Potash, 

0.65 

0.64 

Soda, 

0.43 

5.40 

Water, 

20.18 

18.33 

Total,  99.75  100.37 

Nearly  one-half  the  lime  of  the  original  mineral  was 
thus  substituted  by  soda.  A  loss  of  water  also  occurred. 
The  solution  separated  from  the  mineral,  contained  nothing 
but  soda,  lime,  and  chlorine,  and  the  latter  in  precisely  its 
original  quantity. 

By  acting  on  chabazite  with  dilute  chloride  of  ammo- 
nium (10  grams  to  500  c.c.  of  water)  for  10  days,  the 
mineral  was  altered,  and  contained  3.33  per  cent  of  am- 
monia. Digested  21  days,  the  mineral  yielded  6.94  per 
cent  of  ammonia,  and  also  lost  water. 

These  ammonia-chabazites  lost  no  ammonia  at  212°,  it 
escaped  only  when  the  heat  was  raised  so  high  that  water 
began  to  be  expelled ;  treated  with  warm  solution  of  pot- 
ash it  was  immediately  evolved.  The  ammonia-silicate 
was  slightly  soluble  in  water. 

As  in  the  instances  above  cited,  there  occurred  but  a 
partial  displacement  of  lime.  Eichhorn  made  correspond- 
ing trials  with  solutions  of  carbonates  of  soda  and  am- 


ABSORPTIVE    POWER    OF    THE    SOIL.  347 

monia,  in  order  to  ascertain  whether  the  formation  of  a 
sohible  salt  of  the  displaced  base  limited  the  reaction ; 
but  the  results  were  substantially  the  same  as  before,  as 
shown  by  analyzing  the  residue  after  removing  carbonate 
of  lime  by  digestion  in  dilute  acetic  acid. 

Eichhom  found  that  the  artificial  soda-chabazite  re-ex- 
changed soda  for  lime  when  digested  in  a  solution  of 
chloride  of  calcium ;  in  solution  of  chloride  of  potassium, 
both  soda  and  lime  were  separated  from  it  and  replaced 
by  potash.  So,  the  ammonia-chabazite  in  solution  of  chlo- 
ride of  calcium,  exchanged  ammonia  for  lime,  and  in  so- 
lutions of  chlorides  of  potassium  and  sodium,  both  am- 
monia and  lime  passed  into  the  liquid.  The  ammonia- 
chabazite  in  solution  of  sulphate  of  magnesia,  lost  ammo- 
nia but  not  lime,  though  doubtless  the  latter  base  would 
have  been  found  in  the  liquid  had  the  digestion  been  con- 
tinued longer. 

It  thus  appears  that  in  the  case  of  chabazite  all  the 
protoxide  bases  may  mutually  replace  each  other,  time 
being  the  only  element  of  difference  in  the  reactions. 

Similar  observations  were  made  with  natrolite  (hydrous 
silicate  of  alumina  and  soda,)  as  well  as  with  chlorite  and 
labradorite,  although  in  case  of  the  latter  difficultly  de- 
composable silicates,  the  action  of  saline  solutions  was 
very  slow  and  incomplete. 

Mulder  has  obtained  similar  displacements  with  the 
zeolitic  minerals  stilbite,  thomsonite,  and  j^rehnite.  ( Che- 
mie  der  AcJcerJcrume,  I,  396).  He  has  also  artificially 
prepared  hydrous  silicates,  having  properties  like  those 
of  Way,  and  has  noticed  that  sesquioxide  of  iron  readily 
participates  in  the  displacements.  Mulder  also  found  that 
the  gelatinous  zeolitic  precipitate  obtained  by  dissolving 
hydraulic  cement  in  hydrochloric  acid,  precipitating  by 
ammonia  and  long  washing  with  water,  underwent  the 
same  substitutions  when  acted  upon  by  saline  solutions. 


348  HOW    CKOPS    FEED. 

The  precipitate  he  operated  with,  contained  (water-free) 
in  100  parts: 

Silica 49.0 

Alumina 11.1 

Oxide  of  iron 21.9 

Lime , 6.9 

Magnesia 1.1 

Insoluble  matters  with  traces  of  alkalies,  etc 10.0 

100.0 
On  digesting  portions  of  this  substance  with  solutions 
of  sulphates  of  soda,  potash,  magnesia,  ammonia,  for  a 
single  hour,  all  the  lime  was  displaced  and  replaced  by 
potash — two-thirds  of  it  by  soda  and  nearly  four-fifths  of 
it  by  magnesia  and  ammonia. 

Further  investigations  by  Rautenberg  {Henneberg^s 
Jour,  fur  Landivirthschaft^  1862,  pp.  405-454),  and 
Knop  {Vs.  jSt.,  VII,  57),  which  we  have  not  space  to  re- 
count fully,  have  demonstrated  that  of  the  bodies  possible 
to  exist  in  the  soil,  those  in  the  following  list  do  not  pos- 
sess the  power  of  decomposing  sulphates  and  nitrates  of 
lime,  potash,  ammonia,  etc.,  viz.: 

tD  r  Quartz  sand.  T 

o  I  Kaolinite  (purified  kaolin.)     | 

•g  !  Carbonate  of  lime  (chalk.)      |  These  bodies  have  no  absorptive  effect,  either 

S  1  Humus  (decayed  wood.)  f        separately  or  together. 

g     Hydi-ated  oxide  of  iron.  \  "] 

p^  [Hydrated  alumina,  J  | 

Humate  of  lime,  magnesia,  and  ahmiina.  !  Knop. 

Phosphate  of  alumina.  j 

Gelatinous  silica. 

"  "■      dried  in  the  air.  J 

These  observers,  together  with  Heiden  {Jahreshericht 
ilber  Agriculturchemie^  1864,  p.  17),  made  experiments  on 
soils  to  which  hydrated  silicates  of  alumina,  and  soda,  or 
of  lime,  etc.,  were  added,  and  found  their  absorptive 
power  thereby  increased. 

Rautenberg  and  Heiden  also  found  an  obvious  relation 
to  subsist  between  the  absorptive  powers  of  a  soil  and  cer- 
tain of  its  ingredients.  Rautenberg  observed  that  the  ab- 
sorptive power  of  the  nine  soils  he  operated  vrith  was 
closely  connected  with  the  quantity  of  alumina  and  ox- 


ABSORPTIYE   POWEIl    OF   THE    SOIL.  349 

ide  of  iron  which  the  soils  yielded  to  hydrochloric  acid. 
Heiden  traced  a  similar  relation  between  the  silica  set  free 
by  the  action  of  acids  on  eleven  soils  and  their  absorptive 
power.  Rautenberg  and  Heiden  further  confirmed  what 
Way  and  Peters  had  previously  shown,  viz.,  that  treat- 
ment of  soil  with  acids  diminished  their  absorbent  power. 
These  facts  admit  of  interpretation  as  follows :  Since 
neither  sihca,  hydrated  alumina,  nor  hydrated  oxide  of 
iron,  as  such^  have  any  absorptive  or  decomposing  power 
on  sulphates,  nitrates,  etc.,  and  since  these  bodies  do  not 
ordinarily  exist  as  such  to  much  extent  in  soils,  therefore 
the  connection  found  in  tw^enty  cases  to  subsist  between 
their  amount  (soluble  in  acids)  in  the  soil,  and  the  ab- 
sorptive power  of  the  latter  points  to  a  compound  of 
these  (and  other)  substances  (silicate  of  alumina,  iron, 
lime,  etc.),  as  the  absorptive  agent. 

That  the  absorbing  compound  is  not  necessarily  hydra- 
ted, is  indicated  by  the  fact  that  calcination,  which  must 
remove  water,  though  it  diminishes,  does  not  always  alto- 
gether destroy  the  absorptive  quality  of  a  soil.  (See  p. 
343.)  Eichhorn,  as  already  stated,  found  that  the  anhy- 
drous silicates,  chlorite  and  labradorite,  were  acted  upon 
by  saline  solutions,  though  but  slowly. 

Do  Zeolitic  Silicates,  bydrated  or  otherwise,  exist 
in  tlie  Soil  I — When  a  soil  which  is  free  from  carbonates 
and  salts  readily  soluble  in  water,  is  treated  with 
acetic,  hydrochloric,  or  nitric  acid,  there  is  taken  up  a 
quantity  (several  per  cent.)  of  matter  which,  while  con- 
taining all  the  elements  of  the  soil,  consists  chiefly  of 
alumina  and  oxide  of  iron.  Silica  is  not  dissolved  to  much 
extent  in  the  acid,  but  the  soil  which  before  treatment 
with  acid  contains  but  a  minute  amount  of  uncombined 
silica,  afterwards  yields  to  the  proper  solvent  (hot  solution 
of  carbonate  of  soda)  a  considerable  quantity.  This  is  our 
best  evidence  of  the  presence  in  the  soil  of  easily  decom- 


350 


HOW    CHOPS   PEED. 


posable  silicates.     A  number  of  analyses  which  illustrate 
these  facts  are  subjoined  : 


Water 

Organic  matter 

Sand  and  insoluble  silicates. 

(Clay,  kaolinite) 

f  Silica 

Oxide  of  iron 

Alumina 

Lime 

Magnesia 

Potash 

Soda 

Phosphoric  acid 

Sulphuric  acid 

Carbonic  acid,  chlorine, 
and  loss 


Sandy  Loam. 
Heiden. 


1.613 

2.387 
89.754 
(10.344) 
2.630=! 
1.872 
1.152 
0.161 
0.201 
0.242 
0.034 
0.083 
0.007 

0.047 


1.347 

2.003 

88.782 

(5.762) 

"4.199 

1.630 

1.288 

0.122 

0.240 

0.212 

0.141 

0.034 

0.021 

0.095 


'White 
Clay. 


5. 

Porce- 
lain 
Clay. 

Eautenbekg. 


Bed 
Clay. 


6.15 
none 
58.03 

18.73 
2.11 

12.15 
0.27 
0.29 
0.86 
1.41 

none 


100.000    100.000    100.00     100.00     100.20     100.00 


6.39 
none 
80.51 

6.80 
0.90 
4.35 
0.38 
0.17 


-0.50 


10.36 
none 
89.46 

0.04t 

|-0.14 

0.12 
0.08 


White 
Pottery 

Clay. 
Wat. 


6.18 
none 

58.72 

13.41 
5.38 

13.90 
0.61 
0.43 


1.37 


*  This  soil  yielded  to  solution  of  carbonate  of  soda  before  treatment  with 
acid,  0.340  ^lo  silica. 
t  The  silica  in  this  case  is  the  small  portion  held  in  the  acid  solution. 

The  first  three  analyses  especially,  show  that  the  soils 
to  which  they  refer,  contained  a  silicate  or  silicates  in 
which  iron,  alumina,  lime,  magnesia  and  the  alkalies  ex- 
isted as  bases.  How  much  of  such  silicates  may  occur  in 
any  given  soil  is  impossible  to  decide  in  the  present  state 
of  our  knowledge.  In  the  soil,  free  silica,  is  usually,  if  not 
always  present,  as  may  be  shown  by  treatment  with  solu- 
tion of  carbonate  of  soda,  but  it  appears  difficult,  if  not 
impossible,  to  ascertain  its  quantity.  Again,  hydrated 
oxide  of  iron  (according  to  A.  Miiller  and  Knop)  and  hy- 
drated alumina"^'  (Knop)  may  also  exist,  as  can  be  made 
evident  by  digesting  the  soil  in  solution  of  tartrate  of 
soda  and  potash  (Miiller,  Ys,  jSt.,  IV,  p.  277),  or  in  a  mix- 
ture of  tartrate  and  oxalate  of  ammonia  (Knop,  Vs.  St. 
YIII^p.  41).  Finally,  organic  acids  occur  to  some  ex- 
tent in  insoluble   combinations  with  iron,  alumina,  lime, 


•  More  probably,  highly  basic  carbonates,  or  mixtures  of  hydrates  and  car- 
bonates. 


ABSORPTIVE   POWER    OF   THE    SOIL.  351 

&c.     This  complexity  of  the  soil  effectually  prevents  an 
accurate  analysis  of  its  zeolitic  silicates. 

If  further  evidence  of  the  existence  of  zeolitic  com- 
pounds in  the  soil  were  needful,  it  is  to  be  found  in  con- 
sidering the  analogy  of  the  conditions  which  there  obtain 
with  those  under  which  these  compounds  are  positively 
known  to  be  formed. 

At  Plombieres,  in  France,  the  water  of  a  hot  spring 
(temperature,  140°  F.)  has  flowed  over  and  penetrated 
through  a  mass  of  concrete,  composed  of  bricks  and  sand- 
stone laid  in  lime,  which  was  constructed  centuries  ago  by 
the  Romans.  The  water  contains  about  nine  ten-thou- 
sandths of  solid  matter  in  solution,  a  quantity  so  small  as 
not  to  affect  its  taste  perceptibly.  As  Daubree  has  shown 
(Ann.  des  Mines,  5me.,  Serie,  T.  XIII,  p.  242),  the  cavi- 
ties in  the  masonry  frequently  exhibit  minute  but  well- 
defined  crystals  of  various  zeolitic  minerals,  viz. :  chaba- 
site,  apophyllite,  scolezite,  harmotome,  together  with  hy- 
drated  silicate  of  lime.  These  minerals  have  been  pro- 
duced by  the  action  of  the  water  upon  the  bricks  and  lime 
of  the  concrete,  and  while  a  high  temperature  prevails 
there,  which  probably  has  facilitated  the  crystallization  of 
the  minerals,  as  it  certainly  has  done  the  chemical  altera- 
tion of  the  bricks  and  sandstone,  the  conditions  otherwise 
are  just  those  of  the  soil. 

In  the  soil,  we  should  not  expect  to  find  zeolitic  com- 
binations crystallized  or  recognizable  to  the  eye,  because  the 
small  quantities  of  these  substances  that  could  be  formed 
there  must  be  distributed  throughout  twenty,  fifty,  or 
more  times  their  weight  of  bulky  matter,  which  would 
mechanically  prevent  their  crystallization  or  segregation 
in  any  form,  more  especially  as  the  access  of  water  is  very 
abundant ;  and  the  carbonic  acid  of  the  surface  soil,  which 
powerfully  decomposes  silicates,  would  operate  antago- 
nistically to  their  accumulation. 


352  HOW    CEOPS    PEED. 

The  water  of  the  soil  holds  silica,  lime,  magnesia,  alka- 
lies, and  oxide  of  iron,  often  alumina,  in  solution.  In- 
stances are  numerous  in  which  the  evaporation  of  water 
containing  dissolved  salts  has  left  a  solid  residue  of  sili- 
cates. Thus,  Kersten  has  described  {Jour,  fur  praht, 
Chem.^  22,  1)  a  hydrous  silicate  of  iron  and  manganese 
that  occurred  as  a  hard  incrustation  upon  the  rock,  in  one 
of  the  Freiberg  mines,  and  was  deposited  where  the  water 
leaked  from  the  pumps.  Kersten  and  Berzelius  have  no- 
ticed in  the  evaporation  of  mineral  waters  which  contain 
carbonates  of  lime  and  magnesia,  together  with  silica,  that 
carbonates  of  these  bases  are  first  deposited,  and  finally 
silicates  separate.  {Bischofs  Chem.  Geology,  Cav.  Ed., 
Yol.  1,  p.  5).  Bischof  (/oc.  cit.,  p,  6)  has  found  that  silica, 
even  in  its  most  inactive  form  of  quartz,  slowly  decom- 
poses carbonate  of  soda  and  potash,  forming  silicate  when 
boiled  with  their  aqueous  solutions.  Undoubtedly,  simple 
contact  at  ordinary  temperature  has  the  same  effect, 
though  more  slowly  and  to  a  slight  extent. 

Such  facts  make  evident  that  silica,  lime,  the  alkalies, 
oxide  of  iron  and  alumina,  when  dissolved  in  water,  if  they 
do  not  already  exist  in  combination  in  the  water,  easily 
combine  when  adverse  afiinities  do  not  prevent,  and  may 
react  upon  the  ingredients  of  the  soil,  or  upon  rock  dust, 
with  the  formation  of  zeolites. 

The  "pan,"  which  often  forms  an  impervious  stratum 
under  peat  bogs,  though  consisting  largely  of  oxide  of  iron 
combined  with  organic  acids,  likewise  contains  consider- 
able quantities  of  hydrated  silicates,  as  shown  by  the 
analyses  of  Warnas  and  Michielsen  {Mulder'' s  Chem.  d. 
Ackerlirume,  Bd.  1,  p.  566.) 

Mulder  found  that  when  Portland  cement  (silicate  of 
lime,  alumina,  iron,  etc.)  was  treated  with  strong  hydro- 
chloric acid,  whereby  it  was  decomposed  and  in  part  dis- 
solved, and  then  with  ammonia,  (which  neutralized  and  re- 


AESOEPTIVE    POWER    OF   THE    SOIL.  353 

moved  the  acid,)  tlie  gelatinous  precipitate,  consisting 
chiefly  of  free  silica,  free  oxide  of  iron,  free  alumina,  with 
smaller  quantities  of  lime  and  magnesia,  contained  never- 
theless a  portion  of  silica,  and  of  these  bases  in  combina- 
tion, because  it  exhibited  absorbent  power  for  bases,  like 
Way's  artificial  silicates  and  like  ordinary  soil.  Mere 
contact  of  soluble  silica  or  silicates,  with  finely  divided 
bases,  for  a  short  time^  is  thus  proved  to  be  sufiicient  for 
chemical  union  to  take  place  between  them. 

Recently  precipitated  silicic  acid  being  added  to  lime- 
water,  unites  with  and  almost  completely  removes  the  lime 
from  solution.  The  small  portion  of  lime  that  remains 
in  the  liquid  is  combined  with  silica,  the  silicate  not  being 
entirely  insoluble.  (Gadolin,  cited  in  Storer^s  Diet,  of 
SoliiMUties^  p.  551.) 

The  fact  that  free  bases,  as  ammonia,  potash  and  lime, 
are  absorbed  by  and  fixed  in  soils  or  clays  that  contain  no 
organic  acids,  and  to  a  degree  difierent,  usually  greater  than, 
when  presented  in  combination,  would  indicate  that  they 
directly  unite  either  with  free  silica  or  with  simple  sili- 
cates. The  hydrated  oxide  of  iron  and  alumina  are  in- 
deed, under  certain  conditions,  capable  of  retaining  free 
alkalies,  but  only  in  minute  quantities.     (See  p.  359.) 

The  fact  that  an  admixture  of  carbonate  of  lime,  or  of 
other  lime-salts  wath  the  soil,  usually  enhances  its  absorbent 
power,  is  not  improbably  due,  as  Rautenberg  first  suggest- 
ed, to  the  formation  of  silicates. 

A  multitude  of  additional  considerations  from  the  his- 
tory of  silicates,  especially  from  the  chemistry  of  hydraulic 
cements  and  from  geological  metamorphism,  might  be 
adduced,  were  it  needful  to  fortify  our  position. 

Enough  has  been  written,  however,  to  make  evident 
that  silica,  which  is,  so  to  speak,  an  accident  in  the  plant, 
being  unessential  (we  will  not  affirm  useless)  as  one  of  its 
ingredients,  is  on  account  of  its  extraordinary  capacity  for 
chemical  union  with  other  bodies  in  a  great  variety  of 


354  HOW    CROPS    FEED. 

proportions,  extremely  important  to  the  soil,  and  espe- 
cially so  when  existing  in  combinations  admitting  of  the 
•remarkable  changes  which  have  come  under  our  notice. 

That  we  cannot  decide  as  to  the  precise  composition  of 
the  zeolitic  compounds  which  may  exist  in  the  soil,  is  plain 
from  what  has  been  stated.  We  have  the  certainty  of 
their  analogy  with  the  well-defined  silicates  of  the  miner- 
alogist, which  have  been  termed  zeolites,  an  analogy  of 
chemical  composition  and  of  chemical  properties ;  we  know 
further  that  they  are  likely  to  be  numerous  and  to  be  in 
perpetual  alteration,  as  they  are  subjected  to  the  influence 
of  one  and  another  of  the  salts  and  substances  that  are 
brought  into  contact  with  them ;  but  more  than  this,  at 
present,  we  cannot  be  certain  of. 

Physical  agencies  In  the  phenomena  of  ahsorption. — 

While  the  absorption  by  the  soil  of  potash  or  other  base 
is  accompanied  by  a  chemical  decomposition,  which  Way, 
Rautenberg,  Heiden,  and  Knop's  researches  conclusively 
connect  with  certain  hydrous  silicates  whose  presence  in 
the  soil  cannot  be  doubted,  it  has  been  the  opinion  of 
Liebig,  Brustlein,  Henneberg,  Stohmann  and  Peters, 
that  the  real  cause  of  the  absorption  is  physical,  and  is 
due  to  simple  surface  attraction  (adhesion)  of  the  porous 
soil  to  the  absorbed  substance.  Brustlein  and  Peters  have 
shown  that  bone  and  wood-charcoal,  washed  with  acids, 
absorb  ammonia  and  potash  from  their  salts  to  some  ex- 
tent, and  after  impregnation  with  carbonate  of  lime  to  as 
great  an  extent  as  ordinary  soil.  While  the  reasons  al- 
ready given  appear  to  show  satisfactorily  that  the  ab- 
sorbent power  of  the  soil,  for  bases  in  combination^  re- 
sides in  the  chemical  action  of  zeolitic  silicates,  the  facts 
just  mentioned  indicate  that  the  physical  properties  of  the 
soil  may  also  "exert  an  influence.  Indeed,  the  fixation  of 
free  bases  by  the  soil  may  be  in  all  cases  partially  due  to 
this  cause,  as  Brustlein  has  made  evident  in  case  of  am- 
monia {BoussingauW 8  Agronomie,  etc.,  T.,  II,  p.  153). 


ABSOEPTIVE    POWER    OP    THE    SOIL.  t>55 

Peters  concludes  the  account  of  his  valuable  investiga- 
tion with  the  following  words :  ''"Absorption  is  caused  by 
the  surface  attraction  which  the  particles  of  earth  exert. 
In  the  absorption  of  bases  from  salts,  a  chemical  trans- 
position with  the  ingredients  of  the  soil  is  necessary^ 
lohich  is  m^ade  possible  through  cooperation  of  the  surface 
attraction  of  the  soil  for  the  base^     (Vs.  St.,  II,  p.  151.) 

If  we  admit  the  soundness  of  this  conclusion,  we  must. 
also  admit  that  in  the  soil  the  physical  action  is  exerted 
in  sufficient  intensity  to  decompose  salts,  by  the  hydrated 
silicates  cdone.  We  must  also  allow  that  the  displace- 
ments observed  by  Way  and  Eichhorn  in  silicates,  are 
primarily  due  to  mere  physical  action,  though  they  have 
undeniably  a  chiefly  chemical  aspect. 

That  the  phenomena  are  modified  and  limited  in  certain 
respects  by  physical  conditions,  is  to  be  expected.  The 
facts  that  the  quantity  of  solution  compared  with  the 
amount  of  soil,  the  strength  of  the  solution,  and  up  to 
a  certain  point  the  time  of  contact,  influence  the  degree 
of  absorption,  point  unmistakably  to  purely  physical  in- 
fluences, analogous  to  those  with  whose  action  the  chem- 
ist is  familiar  in  his    daily  experience. 

Absorption  of  Acids.  —  It  has  been  mentioned 
already  that  phosphoric  and  silicic  acids  are  absorbed 
by  soils.  Absorption  of  phosphoric  acid  has  been 
invariably  observed.  In  case  of  silicic  acid,  excep- 
tions to  the  rule  have  been  noticed.  In  very  few  in- 
stances has  the  absorption  of  sulphuric  and  nitric  acids 
or  chlorine,  from  their  compounds,  been  remarked 
hitherto  by  those  who  have  investigated  the  ab- 
sorbent power  of  the  soil.  The  nearly  universal  con- 
clusion has  been  that  these  substances  are  not  subject  in 
any  way,  chemical  or  physical,  to  the  attraction  of  the 
soil.  Yoelcker  was  the  first  to  notice  an  absorption  of 
sulphuric  acid  and  chlorine.  In  his  papers  on  "Farm 
Yard  Manure,"  etc.,  (Jour.  Koy.  Ag.  Soc,  XVIII,  p.  140,) 


356  HOW    CEOPS    FEED. 

and  on  the  "  Changes  which  Liquid  Manure  undergoes  in 
contact  with  different  Soils  of  Known  Composition"  {idem 
XX.,  134-57),  he  found,  in  seven  experiments,  that  dung 
liquor,  after  contact  with  various  soils,  lost  or  gained  acid 
ingredients,  as  exhibited  by  the  following  figures,  in  grains 
per  gallon  :  (loss  is  indicated  by  — ,  gain  by  +)  : 

1  2  34567         A.        B. 

Chloride  of  Potaseium  —8.81    +9.17  —2.74  +2.14  —2.74  +2.55  — I.IQ 

Chloride  of  Sodium. .  .-3.95    —2.43  —7.04  —1.12  —1.10  -1.24  +3.66  —1.89  +19.05 

Sulphuric  Acid +3.32   —4.21  — l.OS  —1.21  —0.27  +1.24  +3.44  +2.26   —0.42 

Silicic  Acid +1.63  +10.33  —1.64  +0.72  +2.76  —0.11  —0.07  undet.  —1.57 

Phosphoric  Acid —         —        —4.23  —3.09  —2.91  —3.38  —0.13  —8.78    —7.71 

We  notice  that  chlorine  was  perceptibly  retained  in 
three  instances,  while  in  the  other  four  it  was,  on  the 
whole,  dissolved  from  the  soil.  Sulphuric  acid  was  re- 
moved from  the  solution  in  four  instances,  and  taken  up 
by  it  in  three  others.  In  four  cases  silica  was  absorbed, 
and  in  three  was  dissolved.  In  his  first  paper.  Professor 
Way  recorded  similar  experiments,  one  with  fiax-steep 
liquor  and  a  second  with  sewage.  The  results,  as  regards 
acid  ingredients,  are  included  in  the  above  table,  A  and  B, 
where  we  see  that  in  one  case  a  slight  absorption  of  chlo- 
rine, and  in  the  other  of  sulphuric  acid,  occurred.  Way, 
however,  regards  these  differences  as  due  to  the  unavoid- 
able errors  of  experiment,  and  it  is  certain  that  in  Voelck-- 
er's  results  similar  allowance  must  be  made.  ISTeverthe- 
less,  these  errors  can  hardly  account  for  the  large  loss  of 
chlorine  observed  in  1  and  3,  or  of  sulphuric  acid  in  2. 

Liebig  found  in  his  experiments  "that  a  clay  or  lime- 
soil,  poor  in  organic  matter,  withdrew  from  solution  of 
silicate  of  potash,  both  silicic  acid  and  potash,  whereas 
one  rich  in  humus  extracted  the  potash,  but  left  the  silicic 
acid  in  solution."     (Compare  pp.  171-5.) 

As  regards  7iitrio  acid ^  Knop  observed  in  a  single  in- 
stance that  this  body  could  not  be  wholly  removed  by 
water  from  a  soil  to  which  it  had  been  added  in  known 
quantity.     He  regards  it  probable  that  it  was  actually 


ABSOKPriYE   POWER    OF   THE    SOIL.  357 

retained  rather  than  altered  to  ammonia  or  some  other 
compound. 

The  fixation  of  acids  in  the  soil  is  unquestionably,  for 
the  most  part,  a  chemical  process,  and  is  due  to  the  for- 
mation of  comparatively  insoluble  compounds. 

Hydrated  oxide  of  iron  and  hydrated  alumina  are 
capable  of  forming  highly  insoluble  compounds  with  all 
the  mineral  acids  of  the  soil.  The  chemist  has  long  been 
familiar  with  basic  chlorides,  nitrates,  sulphates,  silicates, 
phosphates  and  carbonates  of  these  oxides.  Whether  such 
compounds  can  be  actually  produced  in  the  soil  is,  how- 
ever, to  some  extent,  an  open  question,  especially  as  re- 
gards chlorine,  nitric  and  sulphuric  acids.  Their  forma- 
tion must  also  greatly  depend  upon  what  other  substances 
are  present.  Thus,  a  soil  rich  in  these  hydrated  oxides, 
and  containing  lime  and  the  other  bases  in  minuter  quan- 
tity (except  as  firmly  combined  in  form  of  siHcates,)  would 
not  unlikely  fix  free  nitric  acid  or  free  sulphuric  acid  as 
well  as  the  chlorine  of  free  hydrochloric  acid.  When  the 
acids  are  presented  in  the  form  of  salts,  however,  as  is 
usually  the  case,  the  oxides  in  question  have  no  power  to 
displace  them  from  these  combinations.  The  acids,  can- 
not, therefore,  be  converted  into  basic  aluminous  or  iron 
salts  unless  they  are  first  set  free — unless  the  bases  to 
which  they  were  previously  combined  are  first  mastered 
by  some  separate  agent.  In  the  instance  before  referred 
to  where  nitric  acid  disappeared  from  a  soil,  Knop  sup- 
poses that  a  basic  nitrate  of  iron  may  have  been  formed, 
the  soil  employed  being,  in  fact,  highly  ferruginous. 
The  hydrated  oxides  of  iron  and  alumina  do,  however, 
form  insoluble  compounds  ^ith.  pJiosphor to  acid^  and  may 
even  remove  this  acid  from  its  soluble  combinations  with 
lime,  as  Thenard  has  shown,  or  even,  perhaps,  from  its 
compounds  with  alkalies. 

Phosphoric  acid  is  fixed  by  the  soil  in  various  ways. 
When  a    phosphate  of   potash,   for    example,  is  put  in 


358  HOW    CROPS    FEED. 

contact  with  the  soil,  the  base  may  be  withdrawn  by  the 
absorbent  silicate,  and  the  acid  may  unite  to  lime  or  mag- 
nesia. The  phosphates  of  lime  and  magnesia  thus  formed 
are,  however,  insoluble,  and  hence  the  acid  as  well  as  the 
base  remains  fixed.  Again,  if  the  alkali-phosphate  be 
present  in  quantity  so  great  that  its  base  cannot  all  be 
taken  up  by  the  absorbent  silicate,  then  the  hydrated 
oxide  of  iron  or  alumina  may  react  on  the  phosphate,  chemi- 
cally combining  with  the  phosphoric  acid,  while  the  alkali 
gradually  saturates  itself  with  carbonic  acid  from  the  air. 
It  is,  however,  more  likely  that  organic  salts  of  iron  (cre- 
nates  and  apocrenates)  transpose  with  the  phosphate.  So, 
too,  carbonate  of  lime  may  decompose  with  phosphate  of 
potash,  producing  carbonate  of  potash  and  phosphate  of 
lime  (J.  Lawrence  Smith).  Voelcker,  in  a  number  of  ex- 
periments on  the  deportment  of  the  soluble  superphosph.ate 
of  lime  toward  various  soils,  found  that  the  absorption  of 
phosphoric  acid  was  more  rapid  and  complete  with  soils 
containing  much  carbonate  of  lime  than  with  clays  or 
sands. 

All  observers  agree  that  phosphoric  acid  is  but  slowly 
fixed  by  the  soil.  Yoelcker  found  the  process  was  not 
completed  in  2G  days.  Its  absorption  is,  therefore,  mani- 
festly due  to  a  different  cause  from  that  which  completes 
the  fixation  of  ammonia  and  potash  in  48  hours. 

As  to  silicic  acid,  it  may  also,  as  solid  hydrate,  unite 
slowly  with  the  oxides  of  iron  and  with  akimina  (see  Kers- 
ten's  observations,  p.  352).  When  occurring  in  solution,  as 
silicate  of  an  alkali,  as  happens  in  dung  liquor,  it  would 
be  fixed  by  contact  with  solid  carbonate  of  lime,  silicate 
of  lime  being  formed  (Fuchs,  Kuhlmann),  or  by  encoun- 
tering an  excess  of  solutions  of  any  salt  of  lime,  magnesia, 
iron  or  ammonia.  In  presence  of  free  carbonic  acid  in 
excess,  a  carbonate  of  the  alkali  would  be  formed,  and  the 
silicic  acid  would  be  separated  as  such  in  a  nearly  insoluble 


ABSORPTIYE    POWEPw    OF    THE    SOIL.  359 

form.  DuDg  liquor,  rich  in  carbonate  of  potash,  on  the 
other  hand,  would  dissolve  silica  from  the  soil. 

Sulphuric  acid,  existing  in  considerable  quantities  in 
dung  liquor  as  a  readily  soluble  salt  of  ammonia  or  potash, 
would  be  partially  retained  by  a  soil  rich  in  carbonate  of 
lime  by  conversion  into  sulphate  of  lime,  which  is  com- 
paratively insoluble. 

Absorption  of  Bases,  from  their  Hydrates,  Carbonates 
and  SilicateSo — 1.  Incidentally  it  has  been  remarked  that 
free  bases,  among  which  ammonia,  potash,  soda  and  lime 
are  specially  implied,  may  be  retained  by  combiniug  with 
undissolved  silica.  Potash,  soda  (and  ammonia?)  may 
at  once  form  insoluble  compounds  if  the  silica  be  in  large 
proportion  ;  otherwise  they  may  produce  soluble  silicates, 
which,  however,  in  contact  with  lime,  magnesia,  alumina 
or  iron  salts,  will  yield  insoluble  combinations.  As  is 
well  proved,  gelatinous  silica  and  lime  at  once  form  a 
nearly  insoluble  compound.  It  is  probable  that  gelatinous 
silica  may  remove  magnesia  from  solution  of  its  bicarbon- 
ate, forming  a  nearly  insoluble  silicate  of  magnesia. 

2.  It  has  long  been  known  that  hydrated  oxide  of  iron 
and  hydrated  alumina  may  unite  with  and  retain  free 
ammonia,  potash,  etc.  Rautenberg  experimented  with 
both  these  substances  as  freshly  prepared  by  artificial 
means,  and  found  that,  under  similar  conditions, 

10  grms.  of  hydrated      10  grms.  of  hydrated 
oxide  of  iron.  alumina. 

Absorbed  of  free  ammonia     0.046  grm.  0.066  grm. 

"  "  free  potash    -     0.147    "  not  det. 

Long  continued  washing  with  water  removes  the  alkali 
from  these  combinations.  That  oxide  of  iron  and  alumina 
commonly  occur  in  the  soil  in  quantity  sufficient  to  have 
appreciable  effect  in  absorbing  free  alkalies  is  extremely 
improbable. 

Liebig  has  shown  {Ann.  Ch.  u.  Ph.  105,  p.  122,)  that 
hydrated  alumina  imites  with  silicate  of  potash  with  great 


360  HOW    CROPS    FEED. 

avidity  (an  insoluble  douible  silicate  being  formed  just  as 
in  the  experiments  of  Way,  p.  343).  According  to  Liebig, 
a  quantity  of  bydrated  alumina  equivalent  to  2.696  grms. 
of  anhydrous  alumina,  absorbed  from  a  liter  of  solution 
of  silicate  of  potash  containing  1.185  grm.  of  potash  and 
3.000  grm.  of  silica,  fifteen  per  cent  of  the  silicate.  Doubt- 
less hydrated  oxide  of  iron  would  behave  in  a  similar 
manner. 

3.  The  organic  acids  of  humus  are  usually  the  most 
efiective  agents  in  retaining  the  bases  when  the  latter  are 
in  the  free  state,  or  exist  as  soluble  carbonates  or  silic- 
ates. The  properties  of  the  humates  have  been  detailed 
on  page  230.  It  may  be  repeated  here  that  they  form 
with  the  alkalies*  when  the  latter  preponderate,  soluble 
salts,  but  that  these  compounds  unite  readily  to  other 
earthy*  and  metallic*  humates,  forming  insoluble  com- 
pounds. Lime  at  once  forms  an  insoluble  humate,  as 
do  the  metallic  oxides.  When,  as  naturally  happens,  the 
organic  acids  are  in  excess,  their  effect  is  in  all  cases  to 
render  the  soluble  free  bases  or  their  carbonates  nearly 
insoluble. 

In  some  cases,  ammonia,  potash  and  soda  are  absorbed 
more  largely  from  their  carbonates  than  from  their  hy- 
drates. Thus,  in  some  experiments  made  by  the  author, 
a  sample  of  Peat  from  the  New  Haven  Beaver  Meadow 
was  digested  with  diluted  solution  of  ammonia  for  48 
hours,  and  then  the  excess  of  ammonia  was  distilled  off 
at  a  boiling  heat.  The  peat  retained  0,95°  1^  of  this  arKali. 
Another  portion  of  the  same  peat  was  moistened  with 
diluted  solution  of  carbonate  of  ammonia  and  then  dried 
at  212°  until  no  ammoniacal  smell  was  perceptible.  Tliis 
sample  was  found  to  have  retained  1.30°  1^  of  ammonia. 
This  difference  was  doubtless  due  to  the  fact  that  the 


*  In  the  customary  language  of  Chemistry,  potash,  soda,  and  ammonia  are 
alkalies  or  alkali-ljases.  Lime,  magnesia,  and  alumina  are  earths  or  earthy  bases, 
and  oxide  of  iron  and  oxide  of  manganese  are  metallic  bases. 


REVIEW    AND    CONCLUSION.  361 

peat  contained  humate  o/'^/?r/e,  wliich  was  not  affected  by 
the  pure  ammonia,  but  in  contact  with,  carbonate  of  am- 
monia yielded  carbonate  of  lime  and  humate  of  ammonin. 
In  these  cases  the  ammonia  was  m  excess^  and  the  chemical 
changes  were  therefore,  in  some  particulars,  unlike  those 
which  occur  when  the  humus  preponderates. 

Brustlein,  Liebig  and  others  have  observed  that  soils 
rich  in  organic  matter  (forest  mold,  decayed  wood,)  have 
their  absorptive  power  much  enhanced  lij  mixture  with 
carbonate  of  lime. 

Although  Raiitenberg  has  shown  {IIenneberg''s  Journal 
186,  p.  439,)  that  silicate  of  lime  is  probably  formed  when 
ordinary  soils  are  mixed  with  carbonate  of  lime,  it  may 
easily  happen,  in  the  case  of  soils  containing  humus,  that 
humate  of  lime  is  produced,  which  subsequently  reacts 
upon  the  alkali-hydrates  or  salts  with  which  absorption 
experiments  are  usually  made. 


§    6. 

REVIEW  AND  CONCLUSION. 

The  limits  assigned  to  this  work  having  been  nearly 
reached,  and  the  more  important  facts  belonging  to  the 
present  chapter  brought  under  notice,  with  considerable 
fulness,  it  remains  to  sum  up  and  also  to  adduce  a  few 
considerations  which,  may  appropriately  close  the  volume. 
There  are  indeed  a  number  of  topics  connected  with  the 
feeding  of  crops  which  have  not  been  treated  upon,  such, 
especially  as  come  up  in  agricultural  practice ;  but  these 
find  their  place  Jiiost  naturally  and  properly  in  a  discussion 
of  the  improvement  of  the  soil  by  tillage  and  fertilizerSj 
to  which  it  is  proposed  to  devote  a  third  volume. 

What  the  Soil  mast  contain. — In  order  to  feed  crops. 


362 


HOW    CE0P3    FEED. 


the  soil  must  contain  the  ash-ingredients  of  plants,  together 
"with  assimilable  nitrogen-compounds  in  proper  quantity 
and  proportion.  The  composition  of  a  very  fertile  soil  is 
well  exhibited  by  Baumhauer's  analysis  of  an  alluvial  de- 
posit from  the  waters  of  the  Rhine,  near  the  Zuider  Zee, 
in  Holland.  This  soil,  which  produces  large  crops,  con- 
tained— 


Surfac-e. 

15  inches  deep. 

30  inches  d 

Insoluble  silica,  quartz, 

57.640 

51.706 

55.372 

Soluble  silica, 

2.340 

2.496 

2.286 

Alumina, 

1.830 

2.900 

2.888 

Peroxide  of  iron, 

9.039 

10.305 

11.864 

Protoxide  of  iron, 

0.350 

0.563 

0.200 

Oxide  of  manganese, 

0.2S8 

0.354 

0.284 

Lime, 

4.092 

5.096 

2.480 

Magnesia, 

0.130 

0.140 

0.128 

Potash, 

1.026 

1.430 

1.521 

Soda, 

1.972 

2.089 

1.937 

Ammonia,* 

0.060 

0.078 

0.075 

Phosphoric  acid, 

0.466 

0.324 

0.478 

Sulphuric  acid. 

0.896 

1.104 

0.576 

Carbonic  acid, 

6.085 

6.940 

4.775 

Chlorine, 

1.240 

1.302 

1.418 

Humic  acid, 

2.798 

3.991 

3.428 

Creuic  acid. 

0.771 

0.731 

0.037 

Apocrenic  acid. 

0.107 

0.160 

0.152 

Other  organic  matters,  and  com- 

bined water  (nitrates  ?), 

8.324 

7.700 

9.348 

Loss  in  analysis, 

0.540 

0.611 

0.753 

100.000 


100.000 


100.000 


A  glance  at  tlie  above  analyses  shows  the  unusual  rich- 
ness of  this  soil  in  all  the  elements  of  plant-food,  with  ex- 
ception of  nitrates,  which  were  not  separately  determined. 
The  alkalies,  phosphoric  acid,  and  sulphuric  acid,  were 
present  in  large  jDroportion.  The  absolute  quantities  of 
the  most  important  substances  existing  in  an  acre  of  this 
soil  taken  to  the  depth  of  one  foot,  and  assuming  this 


*  The  figures  are  probably  too  high  for  ammonia,  because,  at  the  time  the  analy- 
ses were  made,  the  methods  of  estimating  this  substance  in  the  soil  had  not  been 
studied  sufficiently,  and  the  ammonia  obtained  was  doubtless  derived  in  great 
part  from  the  decomposition  of  humus  under  the  action  of  an  alkali. 


REVIEW    AND    CONCLUSION. 


363 


quantity  to  weigh  3,500.000  lbs.,  (p.  158,)  are  as  follows; 


Ihs. 

Soluble  silica 

81.900 

Lime, 

143.220 

Potash, 

35.910 

Soda, 

68,920 

Ammonia, 

2.100 

Phosphoric  acid. 

16.310 

Sulphuric  acid, 

31.360 

Nitric  acid. 

? 

Quantity  of  Available  Asli-iiigredieiils  necessary  for 
a  Masimum  Crop, — Yf  e  have  already  given  some  of  the 
results  of  Hellriegel's  experiments,  made  for  the  purpose 
of  determining  how  much  of  the  various  elements  of  nu- 
trition are  required  to  produce  a  maximum  yield  of  cereals 
(pp.  215  and  288).  This  experimenter  found  that  74  lbs. 
of  nitrogen  (in  form  of  nitrates)  to  1,000.000  of  soil  was 
sufficient  to  feed  the  heaviest  growth  of  wheat.  Of  his 
experiments  on  the  ash-ingredients  of  crops,  only  those 
relating  to  potash  have  been  published.  They  are  here 
reproduced. 

EFFECTS  OP  VARIOUS  PROPORTIONS  OF  AVAILABLE  POTASH  *  IN 
THE  SOIL  ON  THE  BARLEY  CROP. 


Potash  in 
1,000.000/65.  o/?ot7. 

Yield 

of  Straw  and  Chaff. 

of  Grain. 

Total. 

0 
6 

12 
24 

47 

71 

94 

141 

282 

0.798 
3.869 
5.740 
6.859 
8.195 
9.327 
8.693 
8.764 
8.916 

2.993 
4.695 
7.851 
9.578 
10.097 
9.083 
8.529 
8.962 

6.802 
10.435 
14.710 
17.773 
19.424 
17.776 
17.293 
17.878 

It  is  seen  that  the  greatest  crop  was  obtained  when  71, 
parts  of  potash  were  present  in  1,000.000  lbs.  of  soil.     A 


*  Other  conditions  were  in  all  respects  as  nearly  alike  as  possible. 


364  HOW    CROPS    FEED. 

larger  quantity  depressed  the  yield.  It  is  probable  that  less 
than  71  lbs.  would  have  produced  an  equal  effect,  since  47 
lbs.  gave  so  nearly  the  same  result.  The  ash  composition 
of  barley,  grain,  and  straw,  in  100  parts,  is  as  follows, 
according  to  Zoeller,  (H.  C.  G.,  pp.  150  to  151) : 


Grain. 

Straw. 

Potasb, 

18.5 

12.0 

Soda, 

3.9 

46 

Magnesia, 

7.0 

3.0 

Lime, 

2.7 

7.3 

Oxide  of  iron, 

0.7 

1.9 

Pliosplioric  acid, 

82.4 

6.0 

Sulpliuric  acid. 

2.8 

2.8 

Silica, 

31.1 

59  7 

Clilorine, 

1.1 

2.6 

The  proportion  of  ash  in  the  air-dry  grain  is  2^  per 
cent,  that  in  the  straw  is  5  per  cent,  [Ann.  Ch.  u.  JPh.^ 
CXII,  p.  40).  Assuming  the  average  barley  crop  to  be 
33  bushels  of  grain  at  53  lbs.  per  bushel  =  1,750  lbs.,  and 
one  ton  of  straw,*  we  have  in  the  barley  crop  of  an  acre 
the  following  quantities  of  ash-ingredients  : 


^  s 

1 

-2 

1 

1 

t  . 

ii 

§ 

ley  Grain, 

43.75 

S.l 

1.7 

3.1 

1.2 

0.3 

14.2 

1.2 

0.5 

Straw, 

100.00 

12.0 

4.6 

3.0 

7.3 

1.9 

6.0 

2.8 

2.6 

Total,      143.75        20.1        6.3        6.1        S.5        2.2        20.4        4.0        3.1 

In  the  account  of  Hellriegel's  experiments,  it  is  stated 
that  the  maximum  barley  crop  in  some  other  of  his  trials, 
corresponds  to  8,160  lbs.  of  grain,  or  154  bushels  of  53 
lbs.  each  per  acre.  This  is  more  than  4|-  times  the  yield 
above  assumed. 

The  above  figures  show  that  no  essential  ash-ingredi- 
ent of  the  oat  crop  is  present  in  larger  quantity  than 
potash.     Phosphoric  acid  is  quite  the  same  in  amount, 


*  These  figures  are  employed  by  Anderson,  and  are  based  on  Scotch  statistics. 


REVIEW    AND    CONCLUSION.  365 

while  lime  is  but  one-lialf  as  much,  and  the  other  acids 
and  bases  are  still  less  abundant.  It  follows  then  that  if 
71  lbs.  of  available  potash  in  1,000.000  of  soil  are  enough 
for  a  barley  crop  4|-  times  greater  than  can  ordinarily  be 
produced  under  agricultural  conditions,  the  same  quantity 
of  phosphoric  acid,  and  less  than  half  that  amount  of  lime, 
jetc,  must  be  ample.  CalculatiDg  on  this  basis,  we  give 
in  the  following  statement  the  quantities  required  per 
acre,  taken  to  the  depth  of  one  foot,  to  produce  the  max- 
imum crop  of  Hellriegel  (1),  and  the  quantities  needed 
for  the  average  crop  of  33  bushels  (2).  The  amounts  of 
nitrogen  are  those  which  Hellriegel  found  adequate  to  the 
wheat  crop.     See  p.  289. 


1 

2 

lbs. 

lbs. 

Potash, 

248 

55 

Soda, 

78 

17 

Magnesia, 

76 

17 

Lime, 

105 

33 

Phosphoric  acid, 

250 

55 

Sulphuric 

acid, 

49 

11 

Chlorine, 

38 

8 

Nitrogen, 

245 

54 

If  now  we  divide  the  total  quantities  of  potash,  etc., 
found  in  an  acre,  or  3,500.000  lbs.  of  the  soil  analyzed  by 
Baumhauer,  by  the  number  of  pounds  thus  estimated  to 
be  necessarily  present  in  order  to  produce  a  maximum 
or  an  average  yield,  we  have  the  following  quotients,  which 
give  the  number  of  maximum  barley  crops  and  the  number 
of  average  crops,  for  which  the  soil  can  furnish  the  re- 
spective materials. 

The  Zuidcr  Zee  soil  contains  enough 
Lime  for  1364  maximum  and  6133  average  barley  crops. 

Potash  "     144  "  "       648      " 

Phosphoric  acid  "       65  "  "       293       "  "  " 

Sulphuric        "  "       64  "  "       388       " 

Nitrogen  in  ammonia   "         7  "  "         31       "  "  " 

We  give  next  the  composition  of  one  of  the  excellent 


866  HOW    CHOPS    FEED. 

wheat  soils  of  Mid  Lothian,  analyzed  by  Dr.  Anderson. 
The  air-dry  surface-soil  contained  in  100  parts : 

Silica 71.553 

Alumina 6.935 

Peroxide  of  iron 5.173 

Lime 1.229 

Magnesia 1.083 

Potash 0.354 

Soda 0.433 

Sulphuric  acid 0.044 

Phosphoric  acid 0.430 

Chlorine traces 

Organic  matter 10.198 

Water 2.684 

100.116 

We  observe  that  lime,  potash,  and  sulphuric  acid,  are 
much  less  abundant  than  in  the  soil  from  the  Zuider  Zee. 
The  quantity  of  phosphoric  acid  is  about  the  same.  The 
amount  of  sulphuric  acid  is  but  one-tvv^entieth  that  in  the 
Holland  soil,  and  is  accordingly  enough  for  15  good  bar- 
ley crops. 

Lastly  may  be  instanced  the  author's  analysis  of  a  soil 
from  the  Upper  Palatinate,  which  was  characterized  by 
Dr.  Sendtner,  who  collected  it,  as  "  the  most  sterile  soil  in 
Bavaria." 

Water 0.535 

Organic  matter 1.850 

Silica 0.016 

Oxide  of  iron  and  alumina 1.640 

Lime 0.096 

Magnesia trace 

Carbonic  acid trace 

Phosphoric  acid trace 

Chlorine trace 

Alkalies none 

Quartz  and  insoluble  silicates 95.863 

100.000 

Here  we  note  the  absence  in  weighable  quantity  of 
magnesia  and  phosphoric  acid,  while  potash  could  not  even 


EEVIEW    AXD    COXCLUSIOIs^  367 

be  detected  by  the  tests  emploj^ed.  This  soil  was  mostly 
naked  and  destitute  of  vegetation,  and  its  composition 
shows  the  absence  of  any  crop-producing  power. 

Relative  IsBportaiice  of  the  lagrediests  ®f  tSie  Soil. 
— From  the  general  point  of  view  of  vegetable  nutrition, 
all  those  ingredients  of  the  soil  which  act  as  food  to  the . 
plant,  are  equally  iinportant  as  they  are  equally  indispens- 
able. Absence  of  any  one  of  the  substances  w^hich  water- 
culture  demonstrates  must  be  presented  to  the  roots  of  a 
plant  so  that  it  shall  grow,  is  fatal  to  tlio  productiveness 
of  a  soil. 

Thus  regarded,  oxide  of  iron  is  as  important  as  phos- 
jjhoric  acid,  and  chlorine  (for  the  crops  wdiich  require  it) 
is  no  less  valuable  than  potash.  Practically,  however, 
the  relative  importance  of  the  nutritive  elements  is  meas- 
ured by  tbeir  comparative  abundance.  Those  which,  like 
oxide  of  iron,  are  rarely  deficient,  are  for  that  reason  less 
prominent  among  the  factors  of  a  crop.  If  any  single 
substance,  be  it  phosphoric  acid,  or  sulphuric  acid,  or  pot- 
ash, or  magnesia,  is  lacking  in  a  given  soil  at  a  certain 
time,  that  substance  is  theii  and  for  that  soil  the  most  im- 
portant ingredient.  From  the  point  of  view  of  natural 
abundance,  we  may  safely  state  that,  on  the  whole,  availa- 
ble nitrogen  and  phosphoric  acid  are  the  most  important 
ingredients  of  the  soil,  and  potash,  perhaps,  takes  the  next 
rank.  These  are,  m.ost  commonly,  the  substances  w^hose 
absence  or  deficiency  impairs  fertility,  and  are  those 
which,  when  added  as  fertilizers,  produce  the  most  frequent 
and  remarkable  increase  of  productiveness.  In  a  multi- 
tude of  special  cases,  however,  sulphuric  acid  or  lime,  or 
magnesia,  assumes  the  chief  prominence,  while  in  many  in- 
stances it  is  scarcely  possible  to  make  out  a  greater  crop- 
producing  value  for  one  of  these  substances  over  several 
others.  Again,  those  ingredients  of  the  soil  which  could 
be  spared  for  all  that  they  immediately  contribute  to  the 


368  HOW    CROPS    FEED. 

nourishment  of  crops,  are  often  the  chief  factors  of  fer- 
tility on  account  of  their  indirect  action,  or  because  they 
supply  some  necessary  physical  conditions.  Thus  humus 
is  not  in  any  way  essential  to  the  growth  of  agricultural 
plants,  for  plants  have  been  raised  to  full  perfection  with- 
out it ;  yet  in  the  soil  it  has  immense  value  practically, 
since  among  other  reasons  it  stores  and  supplies  water  and 
assimilable  nitrogen.  Again,  gravel  may  not  be  in  any 
sense  nutritious,  yet  because  it  acts  as  a  reservoir  of  heat 
and  promotes  drainage  it  may  be  one  of  the  most  import- 
ant components  of  a  soil. 

What  tlie  Soil  must  Supply. — It  is  not  sufficient  that 
the  soil  contain  an  adequate  amount  of  the  several  ash-in- 
gredients of  the  plant  and  of  nitrogen,  but  it  must  be  able 
to  give  these  over  to  the  plant  in  due  quantity  and  pro- 
portion. The  chemist  could  without  difficulty  compound 
an  artificial  soil  that  should  include  every  element  of 
plant-food  in  abundance,  and  yet  be  perfectly  sterile.  The 
potash  of  feldspar,  the  phosphoric  acid  of  massive  apatite, 
the  nitrogen  of  peat,  are  nearly  innutritions  for  crops  on 
account  of  their  immobility — because  they  are  locked  up 
in  insoluble  combinations. 

laclicatloKS  of  CheMical  Analysis. — The  analyses  by 
Baumhauer  of  soils  from  the  Zuider  Zee,  p.  362,  give  in  a 
single  statement  their  ultimate  composition.  We  are  in- 
formed how  much  phosphoric  acid,  potash,  magnesia,  etc., 
exist  in  the  soil,  but  get  from  the  analysis  no  clue  to  the 
amount  of  any  of  these  substances  which  is  at  the  dispo- 
sition of  the  present  crop.  Experience  demonstrates  the 
productiveness  of  the  soil,  and  experience  also  shows  that 
a  soil  of  such  composition  is  fertile ;  but  the  analysis  does 
not  necessarily  give  proof  of  the  fact.  A  nearer  approach 
to  providing  the  data  for  estimating  what  a  soil  may  sup- 
ply to  crops,  is  made  by  ascertaining  what  it  will  yield  to 
acids. 


EEYIEW    AND    CONCLUSION.  369 

Boussingault  has  analyzed  in  this  manner  a  soil  from 
Calvario,  near  Tacunga,  in  Equador,  South  America,  which 
possesses  extraordinary  fertility. 

He  found  its  composition  to  be  as  follows : 


Nitrogen  in  organic 

combination, 

0.2i3 

Nitric  acid, 

0.975 

Ammonia, 

0.010 

Pliosphoric  acid, 

' 

0.460 

Clilorine, 

0.395 

Sulphuric  acid, 

0.023 

Carbonic  acid, 

traces 

Potash  and  Soda, 

'Soluble  in  acids. 

1.030 

Lime, 

1.256 

Magnesia, 

0.875 

Sesquioside  of  irou 

2.450 

Sand,  fragments  of  pumice,  and  clay  insoluble  in  acids, 

83.195 

Moisture, 

3.150 

Organic  matters  (les 

5  nitrogen),  undetermined  substances, 

and  loss, 

5.938 

100.000 
This  analysis  is  much  more  complete  in  reference  to  ni- 
trogen and  its  compounds,  than  those  by  Baumhauer  al- 
ready given  (p.  362),  and  therefore  has  a  peculiar  value. 
As  regards  the  other  ingredients,  we  observe  that  phos- 
phoric acid  is  present  in  about  the  same  proportion ;  lime, 
alkalies,  sulphuric  acid,  and  chlorine,  are  less  abundant, 
while  magnesia  is  more  abundant  than  in  the  soils  from 
Zuider  Zee. 

The  method  of  analysis  is  a  guarantee  that  the  one  per 
cent  of  potash  and  soda  does  not  exist  in  the  insoluble 
form  of  feldspar.  Boussingault  found  fragments  of  pumice 
by  a  microscopic  examination.  This  rock  is  vesicular  feld- 
spar, or  has  at  least  a  composition  similar  to  feldspar,  and 
the  same  insolubility  in  acids. 

The  inert  nitrogen  of  the  humus  is  discriminated  from 
that  which  in  the  state  of  nitric  acid  is  doubtless  all  assim- 
ilable, and  that  which,  as  ammonia,  is  probably  so  for  the 
most  part.  The  comparative  solubility  of  the  two  per 
cent  of  lime  and  magnesia  is  also  indicated  by  the  analysis. 
16* 


370  HOW    CROPS    FEED. 

Boussingault  does  not  state  tbe  kind  or  concentration, 
or  temperature  of  the  acid  employed  to  extract  the  soil 
for  the  above  analysis.  These  are  by  no  means  points  of 
indifference.  Grouven  {Iter  S  Ster  Scdzmi'mder  I^ eric hte) 
has  extracted  the  same  earth  with  hydrochloric  acid,  con- 
centrated and  dilute,  hot  and  cold,  with  greatly  different 
results  as  was  to  be  anticipated.  In  1862,  a  sample  from 
an  experimental  field  at  Salzmiinde  was  treated,  after  be- 
ing heated  to  redness,  with  boiling  concentrated  acid  for 
3  hours.  In  1867  a  sample  was  taken  from  a  field  1,000 
paces  distant  from  the  former,  one  portion  of  it  was  treat- 
ed with  boiling  dilute  acid  (1  of  concentrated  acid  to  20 
of  water)  for  3  hours.  Another  portion  was  digested  for 
three  days  with  the  same  dilute  acid,  but  without  apj^lica- 
tion  of  heat.  In  each  case  the  same  substances  were  ex- 
tracted, but  the  quantities  taken  up  were  less,  as  the  acid 
was  weaker,  or  acted  at  a  lower  temperature.  The  follow- 
ing statement  shows  the  composition  of  each  extract,  cal- 
culated on  100  parts  of  the  soil. 

EXTRACT  OF  SOIL  OF  SALZMUNDE. 

Hot  strong  acid.        Rot  dilute  acid.      Cold  dilute  acid. 


Potash, 

.635 

.116 

.029 

Soda, 

.127 

.067 

.020 

Lime, 

1.677 

1.046 

1.09S 

Magnesia, 

.687 

.539 

.237 

Oxide  of  iron  and  alumina, 

,  7.931 

3.180 

.650 

Oxide  of  1 

manganese, 

.030 

.086 

.071 

Sulpliuric 

acid, 

.059 

.039 

.020 

Pliosptioric  acid, 

.059 

.091 

.057 

Silica, 

1.785 

.234 

.175 

Total,  12.990  5.398  2.357 

The  most  interesting  fact  brought  out  by  the  above  fig- 
ures, is  that  strong  and  weak  acids  do  not  act  on  all  the 
ingredients  with  the  same  relative  power.  Comparing  the 
quantities  found  in  the  extract  by  cold  dilute  acid  with 
those  which  the  hot  dilute  acid  took  up,  we  find  that  the 
latter  dissolved  5  times  as  much  of  oxide  of  iron  and 
alumina,  4  times  as  much  potash,  3  times  as  much  soda, 


KEVIEW    AND    CON^CLUSIOX.  371 

twice  the  amount  of  magnesia,  sulphuric  acid,  and  phos- 
phoric acid,  and  the  same  quantity  of  lime.  These  facts 
show  how  very  far  chemical  analysis  in  its  present  state 
is  from  being  able  to  say  definitely  what  any  given  soil 
can  supply  to  crops,  although  we  owe  nearly  all  our  pre- 
cise knowledge  of  A^egetable  nutrition  directly  or  indi- 
rectly to  this  art. 

The  solvent  effect  of  water  on  the  soil,  and  the  direct 
action  of  roots,  have  been  already  discussed  (pp.  309  to 
328).  It  is  unquestionably  the  fact  that  acids,  like  pure 
water  in  Ulbricht's  exj^eriments  (p.  324),  dissolve  the 
more  the  longer  they  are  in  contact  with  a  soil,  and  it  is 
evident  that  the  question :  How  much  a  particular  soil  is 
able  to  give  to  crops  ?  is  one  for  which  we  not  only  have 
no  chemical  answer  at  the  present,  but  one  that  for  many 
years,  and,  perhaps,  always  can  be  answered  only  by  the 
method  of  experience — by  appealing  to  the  crop  and  not 
to  the  soil.  Chemical  analysis  is  competent  to  inform  us  very 
accurately  as  to  the  ultimate  composition  of  the  soil,  but  as 
regards  its  proximate  composition  or  its  chemical  consti- 
tution, there  remains  a  vast  and  difficult  Unknown,  which 
will  yield  only  to  very  long  and  laborious  investigation. 

Mainteiiaiice  of  a  Supply  of  Flant-food, — By  the  recip- 
rocal action  of  the  atmosphere  and  the  soil,  the  latter 
keejDS  up  its  store  of  available  nutritive  matters.  The 
difficultly  soluble  silicates  slowly  yield  alkalies,  lime,  and 
magnesia,  in  soluble  forms ;  the  sulphides  are  converted 
into  sulphates,  and,  generally,  the  minerals  of  the  soil  are 
disintegrated  and  fluxed  under  the  influence  of  the  oxy- 
gen, the  water,  the  carbonic  acid,  and  the  nitric  acid  of 
the  air,  (pp.  122-135).  Again,  the  atmospheric  nitrogen 
is  assimilated  by  the  soil  in  the  shape  of  ammonia,  ni- 
trates, and  the  amide-like  matters  of  humus,  (pp.  254-265). 

The  rate  of  disintegration  as  well  as  that  of  nitrifica- 
tion depends  in  part  upon  the  chemical  and  physical  char- 
acters of  the  soil,  and  partly  upon  temperature  and  mete- 


372  HOW    CF.OPS    F£ED. 

orological  conditions.  In  tlie  tropics,  both  these  processes 
go  on  more  vigorously  than  in  cold  climates. 

Every  soil  has  a  certain  inherent  capacity  of  production 
in  general,  y/liicli  is  chiefly  governed  by  its  povrer  of  sup- 
plying plant-food,  and  is  designated  its  "  natural  strength." 
The  rocky  hill  ranges  of  the  Housatonic  yield  once  in 
30  years  a  crop  of  wood,  the  value  of  which,  for  a  given 
locality  and  area,  is  nearly  uniform  from  century  to  cen- 
tury. Under  cultivation,  the  same  uniformity  of  crop  is 
seen  when  the  conditions  remain  unchanged.  Messrs. 
Lawes  and  Gilbert,  in  their  valuable  experiments,  have 
obtained  from  "  a  soil  of  not  more  than  average  wheat- 
j^roducing  quality,"  without  the  application  of  any  ma- 
nure, 20  successive  crops  of  wheat,  the  first  of  which  was 
15  bushels  per  acre,  the  last  17^  bushels,  and  the  average 
of  all  161  bushels.  {Jour.  Roy.  Ag.  jSoc.  of  Eng.,  XXY, 
490.)  The  same  investigators  also  raised  barley  on  the 
same  field  for  16  years,  each  year  applying  the  same  quan- 
tity and  kinds  of  manure,  and  obtaining  In  the  first  8 
years  (1852-59)  an  average  of  44|-  bushels  of  grain  and 
28  cwt.  of  straw ;  for  the  second  8  years  an  average  of  51|- 
bushels  of  grain  and  29  cwt.  of  straw;  and  for  the  16 
years  an  average  of  48i-  bushels  of  grain  and  28i-  cwt.  of 
straw.  {Jour,  of  Bath  and  West  ofUng.Ag.Soc,  XYI,214.) 

The  wheat  experiments  show  the  natural  capacity  of 
the  Kothamstead  soil  for  producing  that  cereal,  and  de- 
monstrate that  those  matters  which  are  annually  removed 
by  a  crop  of  16^  bushels,  are  here  restored  to  availability 
by  weathering  and  nitrification.  The  crop  is  thus  a 
measure  of  one  or  both  of  tlieso  processes."'  It  is  probable 

*  In  the  experiments  of  Lawes  and  Gilbert  it  was  found  that  phosphates,  sul- 
phates, and  carbonates  of  lime,  potash,  magnesia,  and  soda,  raised  the  produce 
of  wheat  but  2  to  3  bushels  per  acre  above  the  yield  of  the  unmanured  soil,  while 
sulphate  and  muriate  of  ammonia  increased  the  crop  6  to  10  bushels.  This  re- 
sult, obtained  on  three  soils,  viz.,  at  Rothamstead  in  Herts,  Holkham  in  Nor- 
folk, and  Rodmersham  in  Kent,  the  experiments  extending  over  periods  of  8,  3, 
and  4  years,  respectively,  shows  that  these  soils  were,  for  the  wheat  crop,  rela- 
tively deficient  in  assimilable  nitrogen.  The  crop  on  the  unmanured  soil  was 
therefore  a  measure  of  nitrification  rather  than  of  mineral  disintegration. 


KEYIEW    AND    CONCLUSIOX.  373 

that  this  native  power  of  producing  wheat  will  last  unim- 
paired for  years,  or,  perhaps,  centuries,  provided  the  depth 
of  the  soil  is  sufficient.  In  time,  however,  the  silicates 
and  other  compounds  whose  disintegration  supplies  alka- 
lies, phosphates,  etc.,  must  become  relatively  less  in  quan- 
tity compared  with  the  quite  inert  quartz  and  alumina- 
silicates  which  cannot  in  any  way  feed  plants.  Then  the 
crop  will  fall  ofi",  and  ultimately,  if  sufficient  time  be  al- 
lowed, the  soil  v/ill  be  reduced  to  sterility. 

Other  things  being  equal,  this  natural  and  durable  pro- 
ductive pov/er  is  of  course  greatest  in  those  soils  which 
contain  and  annually  supply  the  largest  proportions  of 
plant-food  from  their  entire  mass,  those  which  to  the  great- 
est extent  originated  from  good  soil-making  materials. 

Soils  formed  from  nearly  pure  quartz,  from  mere  chalk, 
or  from  serpentine  (silicate  of  magnesia),  are  among  those 
least  capable  of  maintaining  a  supply  of  food  to  crops. 
These  poor  soils  are  often  indeed  fairly  productive  for  a 
few  years  when  first  cleared  from  the  forests  or  marshes ; 
but  this  temporary  fertility  is  due  to  a  natural  manuring, 
the  accumulation  of  vegetable  remains  on  the  surface, 
which  contains  but  enough  nutriment  for  a  few  crops  and 
wastes  rapidly  under  tillage. 

ExhaEStlon  ©f  tlie  Soil  in  the  language  of  Practice  has 
a  relative  meaning,  and  signifies  a  reduction  of  producing 
power  below  the  point  of  remuneration.  A  soil  is  said  to 
be  exhausted  when  the  cost  of  cropping  it  is  more  than 
the  crops  are  worth.  In  this  sense  the  idea  is  very  indef- 
inite since  a  soil  may  refuse  to  grov/  one  crop  and  yet  may 
give  good  returns  of  another,  and  because  a  crop  that  re- 
munerates in  the  vicinity  of  active  demand  for  it,  may  be 
worthless  at  a  little  distance,  on  account  of  difficulties  of 
transportation.  The  speedy  and  absolute  exhaustion  of  a 
soil  once  fertile,  that  has  been  so  much  discussed  by  spec- 
ulative writers,  is  found  in  their  writings  only,  and  does 
not  exist  in  agriculture.     A  soil  may  be  cropped  below  tlie 


374  HOW    CROPS    FEED. 

point  of  remuneration,  but  the  sterility  thus  induced  is  of 
a  kind  that  easily  yields  to  rest  or  other  meliorating  agen- 
cies, and  is  far  from  resembling  in  its  permanence  that 
which  depends  upon  original  poverty  of  constitution. 

SignificaBce  ®f  tlie  Absorptive  Quality,— Disintegration 
and  nitrificiition  would  lead  to  a  waste  of  the  resources 
of  fertility,  were  it  not  for  the  conserving  effect  of  those 
physical  absorptions  and  chemical  combinations  and  re- 
placements which  have  been  described.  The  two  least 
abundant  ash-ingredients,  viz.,  potash  and  phosphoric  acid, 
if  liberated  by  the  weathering  of  the  soil  in  the  form  of 
phosphate  of  potash,  would  suffer  speedy  removal  did  not 
the  soil  itself  iix  them  both  in  combinations,  which  are  at 
once  so  soluble  that,  while  they  best  serve  as  plant-food, 
they  cannot  ordinarily  accumulate  in  quantities  destruct- 
ive to  vegetation,  and  so  insoluble  that  the  rain-fall  cannot 
wash  them  off  into  the  ocean. 

The  salts  that  are  abundant  in  springs,  rivers,  and  seas, 
are  naturally  enough  those  for  which  the  soil  has  the  least 
retention,  viz.,  nitrates,  carbonates,  sulphates,  and  hydro- 
chlorates  of  lime  and  soda. 

The  constituents  of  these  salts  are  either  required  by 
vegetation  in  but  small  quantities  as  is  the  case  with  chlo- 
rine and  soda,  or  they  are  generally  speaking,  abundant 
or  abundantly  formed  in  the  soil,  so  that  their  removal 
does  not  immediately  threaten  the  loss  of  productiveness. 
In  fact,  these  more  abundant  matters  aid  in  putting  into 
circulation  the  scarcer  and  less  soluble  insjredients  of 
crops,  in  accordance  with  the  general  law  established  by 
the  researches  of  Way,  Eichhorn,  and  others,  to  the  effect 
that  any  base  brought  into  the  soil  in  form  of  a  freely  sol- 
uble salt,  enters  somewhat  into  nearly  insoluble  combina- 
tion and  liberates  a  corresponding  quantity  of  other  bases. 

"  The  great  beneficent  law  regulating  these  absorptions 
appears  to  admit  of  the  following  expression  :  those  bodies 
which  are  most  rare  and  precious  to  the  growing  plant  are 


EEYIEW    AND    COXCLUSION.  375 

by  the  soil  converted  into^  and  retained  in ^  a  condition  not 
of  absolute^  but  of  relative  insolubility^  cmd  are  kept  avail- 
able to  the  plant  by  the  continual  circulation  in  the  soil 
of  the  more  abundant  saline  matters. 

"  The  soil  (speaking  in  the  widest  sense)  is  then  not  only 
the  ultimate  exhaustless  source  of  mineral  (fixed)  food, 
to  vegetation,  but  it  is  the  storehouse  and  conservatory 
of  this  food,  protecting  its  OTvn  resources  from  waste  and 
from  too  rapid  use,  and  converting  the  highly  soluble 
matters  of  animal  exuvis8  as  well  as  of  artificial  refuse 
(manures)  into  permanent  supplies."* 

By  absorption  as  well  as  by  nitrification  the  soil  acts 
therefore  to  prej^are  the  food  of  the  plant,  and  to  present 
it  in  due  kind  and  quantity. 


*  The  author  quotes  here  the  concluding  paragraphs  of  an  article  by  him  "  On 
Some  points  of  Agricultural  Science,"  from  the  Avierican  Journal  of  Science  and 
Arts,  May,  1859,  (p.  85),  which  have  historic  interest  in  being,  so  far  as  he  is 
aware,  the  earliest,  broad  and  accurate  generalization  on  record,  of  the  facts  of 
soil-absorption. 

NOTICE    TO    TEACHERS. 

At  the  Author's  request,  Mr.  Louis  Stadtmuller,  of  New  Haven, 
Conn.,  will  undertake  to  furnish  collections  of  the  minerals  and  roclv^ 
which  chiefly  compose  soils  (see  pp.  108-122),  suitable  for  study  and 
illustration,  as  also  the  apparatus  and  materials  needful  for  the  chemical 
experiments  described  iu  "How  Crops  Grow." 


JUST    PUBIilSKSB. 


TALKS    ON    MANUSES. 

By  JOSEPH  HAKI?iS,  M,  S. 

Of  JfoJ'eion  F<irm,  llocheater.  New   Yorlc.     AutJini^  of  "  Walks  and  Talks  o?i  the 
Farm"  "  Talks  07i  Farm  Crops,''  "ZTarriS  on  the  Pig,'"  etc. 


While  we  have  no  lack  of  treatises  upon  artificial  fertilizers,  there  is  no  work 
in  which  the  main  stay  of  tlie  farm— the  manure  made  upon  tlie  farm — is  treated  so 
satisfactorily  or  thoroughly  as  in  this  volume.     Starting  with  the  question, 

the  author,  well-known  on  both  sides  of  the  water  by  his  writings,  runs  through  in 
suflcLcient  detail  every  source  of  manure  on  the  farm,  discussing  the  methods  of 
making  rich  manure  ;  the  proper  keeping  and  applying  it,  and  especially  the 

"USES    OF    MiAT^XJUiE, 

and  the  effects  of  different  artificial  fertilizers,  as  compared  with  farm-yard 
manure,  upon  different  crops.  In  this  he  makes  free  use  of  the  striking  series  of 
esperiments  instituted  years  ago,  and  still  continued,  by  Lawes  and  Gilbert,  of 
Rothamsted,  England.    The 

in  which  the  results  of  these  esperiments  are  given,  are  here  for  the  first  time 
made  accessible  to  the  American  farmer.  In  fact,  there  is  scarcely  any  point  re- 
lating to  fertilizing  the  soil,  including  the  suitable  manures  for  special  crops, 
that  is  not  treated,  and  while  the  teachings  are  founded  upon  the  most  elaborate 
scientific  researches,  they  are  so  far  divested  of  the  technical  language  of  science 
as  to  commend  themselves  to  farmers  as  eminently  "•practical."  It  is  not  often 
that  the  results  of  scientific  investigations  are  presented  in  a  manner  so  thoroughly 
popular.  12rao.     PRICE,  POST-PAID,  $1.50. 

ORAKGE  JUBD  COMPAHY,  245  Broadway,  New  York, 


JUST   PUBI.ISHED, 


This  is  a  valuable  work  which  meets  the  wants  of  persons  of  moderate  means, 
and  will,  it  is  believed,  prove  one  of  the 

Most  Popular  Architectural  Books 

ever  issued.  It  gives  a  wide  range  of  design,  from  a  dwelling  costing  $250  up  tc- 
$8,000,  and  adapted  to  farm,  village,  and  tov/n  residences.  Nearly  aH  of  these 
plans  have  been  tested  by  practical  workings.  Thejr  provide  for  heating,  ventila- 
tion, etc.,  and  give  a  large  share  of  what  are  called  Modern  Improvements.  One 
feature  of  the  worlj;  imparts  a  value  over  any  similar  publications  of  the  kind  that 
Ave  have  seen.    It  gives  an 

Estimate  of  the  Quantity  op  Every  Article  Used 

in  the  construction,  and  the  cos^  of  each  material  at  the  time  the  building  was 
erected,  or  tlie  design  made.  Even  if  prices  vary  from  time  to  time,  one  can, 
from  these  data,  ascertain  within  a  few  dollars,  the  probable  cost  of  constructing 
any  one  of  the  buildings  here  presented. 

PROFUSELY   ILLUSTKATED.     12mo.     PRICE,  POST-PAID,  $1.50. 

ORAIfGE  JUBB  COMPAHY,  245  Broadway,  New  York. 


jyST    PUBLiSI^ED. 


Winter  Greeneries 

IT  HOME, 

By    Rev,    E.   A.    JOHNSON,  D.   D. 

Author  of  "  Half  Hour  Studies  of  Life,''  etc.,  etc. 


This  Volume  differs  from  most  otiier  works  on  winter  gardening,  In  giving 
the  results  of  actual  practice.  The  author  for  several  years  past  has  found  re- 
creation In  heautifying  his  study  with  plants  ;  his  work  has  resulted  in  so 
much  enjoyment  to  himself  and  his  friends  that  he  has  been  induced  to  tell 
what  he  did,  and  how  he  did  it.  The  book  .is  not  a  mere  dry  set  of  directions, 
but  its  teachings  are  presented  in  the  pleasant  form  of  letters  to  some  young 
ladies,  who,  having  witnessed  the  author's  success,  have  asked  his  instruction, 
and  this  allows  a  genial  personality  to  pervade  the  work,  and  makes  it  withal 
readable,  as  well  as  instructive.  It  is  a  most  excellent  guide  to  successful  win- 
ter-gardening, as  suited  to  American  homes,  with  our  peculiar  domestic  sur- 
roundings, and  those  who  follow  its  teachings  will  reach  a  satisfactory  measure 
of  success.  The  ensfravings  include  several  representations  of  the  author's  study 
FINELY   ILLUSTKATED.     12mo.    PRICE,  POST-PAID,   $1. 

OEANGE  JUDD  COMPANY,  245  Broadway,  Hew  York. 


FARM-GARDENING 


A^D 


BY  FRANCIS  BRILL. 


Orange  Judd  &  Co.  have  added  to  their  splendid  catalogue  of  agricultural 
books  ''  Farni-Gardeuing  and  Seed-Growing,"  by  Francis  Brill;  it  is  practical, 
plain,  compk'te,  and  satisfactory,  so  that  for  a  small  amount  of  money  a  great 
deal  of  desirable  information  can  be  obtained.  If  there  is  any  firm  anywhere 
Avhich  is  to-day  disseminatinij  so  much  knowledge  in  regard  to  tilling  of  the 
soil,  as  this  same  said  firm  of  Orange  Judd  &  Co.,  we  wifl  present  u  medal  to 
our  infovmei:—Watc/wia>i  and  Refiectoi\  (Boston.) 

The  want  occasionally  expressed  to  us  of  a  work  on  the  cognate  subjects 
above  named,  (Farm-Gardeuing  and  Seed-Growing,)  is  now  met  in  a  book 
tinder  tliis  title,  from  the  pen  of  Mr.  Francis  Brill,  formerly  a  market-gardener 
and  seed-grower  at  Newark,  N.  J.,  and  at  present  engaged  in  raising  seeds  at 
Mattituck,  L.  I.  Its  directions  are  concise  and  practical,  covering  those  points. 
on  which  a  beginner  is  most  likely  to  require  information. —  Country  Gentleman. 

It  seems  to  be  a  very  sensible,  practical  work  by  a  practical  man.  Mr. 
BrilTs  father  was  a  gardener;  and  he  himself  has  had  an  extensive  experience, 
and  he  talks  about  what  he  knows,  which  is  more  than  can  be  said  of  many 
authors  of  industrial  works.— J/oore'.?  Rural  New-Yorker. 

There  can  be  no  question  that  this  farm-gardening  can  be  made  in  many  dis- 
tricts of  the  Southern  Atlantic  States,  especially  near  the  coast,  far  more  profit- 
able than  growing  the  ordinary  staple  crops.  In  connection  with  producing 
the  vegetables,  the  growing  and  saving  their  seeds  receive  minute  attention.— 
American.  Farmer,  (Baltimore.) 

This  industry  is  now  occupying  the  attention  of  many  persons  who  sell 
their  pjroducts  to  the  great  seed-houses,  and  novices  who  have  the  facilities, 
and  wish  to  enter  upon  the  business,  will  find  in  this  book  just  the  hints 
n&QOiQCi.—SjJringfieldliepublican. 

Mr.  Brill  has  been  a  successful  farm-gardener  and  seed-grower  for  a  number 
of  years,  and  gi\^es  in  a  clear  and  concise  form  the  knowledge  he  has  gained. 
. .  .".It  gives  the  best  method  of  manuring,  planting,  and  cultivating  every  veg- 
etable sold  in  market— in  short,  every  thing  required  to  be  known,  plainly  and 
fully— and  should  be  in  the  hands  of  every  one  who  cultivates  so  much  as  a 
rod  of  land  for  family  use,  pleasure,  or  ■gvoQ.t,— Suffolk  (L.  I.)  Times. 

The  seal  of  Orange  Judd  &  Co.  upon  an  agricultural  publication  is  sufficient 
guarantee  of  its  worth.  Francis  Brill's  book,  published  by  them,  is  a  very 
complete  work,  giving  plain,  minute  instructions  as  to  raising,  taking  care  of, 
and  bringing  to  market,  those  vegetables  which  are  most  in  demand  ia  the 
large  cities,  and  those  seeds  which  are  being  called  for  throughout  the  country. 
— JSf.  Y.  Evening  Jlail. 

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GAEBEIflMG   FOE  PROFIT: 

A  GUIDE  TO  THE  SUCCESSFUL  CULTIVATION  OF  THE 

MAEKET  Am  FAMILY  GAUDEll', 

By  Peter  Hendeeson. 

IPITsTEIj-IZ'     iil.Xjt:jstr,a.teid. 

This  •work  has  had  a  constant  and  remarkable  sale  ever  since  it  Avas  issued,  and 
the  later  enlarged  and  revised  edition  is  as  well  received  as  was  the  first.  It  was 
the  first  work  on  Market  Gardening  ever  published  in  this  countrJ^  Its  author  is 
Avell  known  as  a  market  gardener  of  manj'-  years'  successful  experience.  In  this 
work  he  has  recorded  this  experience,  and  given  without  rcservatiou,  the  methods 
necessary  to  the  profitable  culture  of  the 

3^a.iijk:et    G5-A.iiT>E:isr. 

It  is  a  work  for  which  there  was  an  urgent  demand  before  its  issue,  and  one 
which  commends  itiself,  not  only  to  those  who  grow  vegetables  for  sale,  but  to  the 
cultivator  of  the 

to  whom  it  presents  methods  quite  difterent  from  the  old  ones  generally  practiced. 
It  is  an  ORIGINAL  and  pukely  AMERICAN  work,  and  not  made  up  as  books  on  gar- 
dening too  often  are,  by  quotations  from  foreign  authors. 

Every  thing  is  made  perfectly  plain,  and  the  subject  treated  in  all  its  details, 
from  the  selection  of  the  soil  to  preparing  the  products  for  market. 

CONTENTS. 

Men  fluted  for  tlie  Business  of  Gardening. 

The  Amount  of  Capital  Kegviired,  and 

"Working  Force  per  Acre. 

Profits  of  Market  Gardening. 

Location,  Situation,  and  Laying  Out. 

Soils,  Drainage,  and  Preparation. 

Manures,    Implements. 

Uses  and  Management  of  Cold  Frames. 

Formation  and  Management  of  Hot-beds. 

Forcing  Pits  or  Greenhouses. 

Seeds  and  Seed   Raising. 

How,  "When,  and  "Where  to  Sow  Seeds. 

Transplanting  Insects. 

Packing  of  "Vegetables  for  Shipping. 

Preservation  of  Vegetables  in  "Winter. 

Vegetables,  their  Varieties  and  Cultivation. 

In  the  last  chapter,  the  most  valuable  kinds  are  described,  and  the  culture 
proper  to  each  is  given  in  detail. 

Sent   post-paid,    price   $1.50. 
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THE  TIM  BUNKER  PAPERS  , 

Or,    YANKEE    FAK^ii^C- 

BT 

TIMOTHY    BUNKER,    Esq.. 

OF  HOOKERTOWN,  CT. 

With  Illustrations  hij  Hoppin, 


CONTENTS, 


A  Stroke  of  Economy. 

Ornamental  Trees. 

Timothy  Bunker,  Esq. 

View  of  the  Bird  Lav/. 

Guano  in  the  Hill. 

On  Moss  Bunkers. 

On  Subsoiling. 

Going  to  the  Fair. 

In  Tall  Clover. 

On  Horse  Racing. 

At  the  Farmers'  Club. 

On  an  Old  Saw. 

Book  Farming  in  Hookertown. 

Pasturinir  Cattle  in  Roads. 

The  Weaker  Brethren. 

Curing  a  Horse  Pond. 

Domesticities  at  Tim  Bunker's. 

Takes  a  Journey. 

On  Farm  Roads. 

A  New  Manure. 

Losijig  the  Premium. 

A  New  Enterprise. 

Making  Tiles. 

The  Clergy  and  Farming. 

Women  Horse  Racing. 

Beginning  Life. 

An  Apology  for  Tim  Bunker 

On  County  Fairs. 

At  Home  A^in. 

On  Raising  Boys. 

On  Raising  Girls. 

A  New  Case  of  the  Black  Art. 

A  Letter  from  Neighbors. 

The  Shadtown  Parsonage. 

Views  of  Dress. 

A  Rustic  Wedding. 

Saving  a  Sixpence. 

On  Giving  Land  a  Start. 

On  Giving  Boys  a  Start. 

A  Tile  in  the  Head. 

Jake  Frink  Sold. 

The  New- York  Central  Park. 

On  Irrigation. 


84. 


Feeding  with  Oil  Meal. 

The  Farmers'  Club. 

On  Bad  Water. 

Cattle  Disease. 

On  Seed. 

On  Breastworks  in  War. 

Lightning  Rods. 

Buying  a  Farm. 

Topdressing  and  Feeding  After 

math. 
Painting  Buildings. 
The  Value  of  Muck. 
On  Family  Horses. 
The  Horn-ail. 
A  Commentary  on  Roots. 
Stealing  Fruit  and  Flowers. 
The  Cost  of  Pride. 
Swamps  Turning  Indian. 
Tim  Bunker  in  his  Garden. 
On  Running  Astern. 
On  Extravagance. 
The  Farmer^s  Old  Age. 
On  Sheep  Traps. 
Old  Style  Housekeeping. 
On  Keeping  a  Wife  Comfortable 
Starting  a  Sugar  Mill. 
Reasons  against  Tobacco. 
Trip  to  Washington. 
The  Sanitary  Commission. 
Raid  among  the  Pickle  Patches 
Raid  among  the  Pickle  Patches. 
On  Striking  He. 
Visit  to  Titus  Oaks,  Esq. 
The  Pickle  Fever  in  Hookertown 
On  Curing  Pickles   and  Eating 

them. 
The  Cotton  Fever  and  Emigration. 
The  Cotton  Fever  and  Emigratioa 
The  Food  Question. 
On  Jim  Crow. 
The  Eight-Hour  Law. 
Base  Ball  Clubs. 
The  Rise  of  Real  Estate. 


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THE  PRACTICAL 

POULTRY    KEEPER. 

A  Complete  and  Standard  Guide  to  the 

MANAGEMEFT    OF    FOULTEY, 

For  Domestic  Use,  the  Markets,  or  Exhibition. 

BEAUTIFULLY     ILLUSTRATED. 

By  L.  WRIGHT. 


OOINTTEJ^NTTS. 


SECTION  I.— The  Generai.  Man- 
agement OF  Domestic  Poultry 
AviTH  A  View  to  Profit. 

Chap.  I.— Houses  and  Runs ;  and 
the  appliances  necessaiy  to  keep- 
ing Poultry  with  success. 

Chap.  II.— On  the  System  of  Opera- 
tions and  the  Selection  of  Stock. 

Chap.  III.— The  Feeding  and  Gener- 
al Management  of  Adult  Fowls. 

Chap.  IV. — Incubation. 

Chap.  V.— The  Rearing  and  Fatten- 
ing of  Chickens. 

Chap.  VI.— Diseases  of  Poultry. 

SECTION  II.— The  Breedino  and 
Exhibition  of  Prize  Poultry. 

Chap.  VII.— Yards  and  Accommo- 
dation adapted  for  Breeding  Prize 
Poultry. 

Chap.  VIII.— On  the  Scientific  Prin- 
ciples of  Breeding,  and  the  Effects 
of  Crossing. 

Chap.  IX.— On  the  Practical  Selec- 
tion and  Care  of  Breeding  Stock, 
and  the  Rearing  of  Chickens  for 
Exhibition. 

Chap.  X. — On  "  Condition,"  and  the 
Preparation  of  Fowls  for  Exhibi- 
tion ;  and  various  other  matters 
connected  with  Shows. 

SECTION  III.— Different  Breeds 
.     OF  Fowls;   their  Characteris- 
tic Points,  with  a  Comparison 
of  their  Merits  and  Principal 
Defects. 


Chap.  XI.— Cochin  Chinas  or  Shang. 

haes. 
Chap.  XII.— Brahma  Pootras. 
Chap.  XIII.— Malays. 
Chap.  XIV.— Game. 
Chap.  XV.— Dorkings. 
Chap.  XVI.— Spanish. 
Chap.  XVII.— Hamburglis. 
Chap.  XVIII.— Polands. 
Chap.  XIX.— French  Breeds. 
Chap.  XX. — Bantams. 
Chap.  XXI.— The  "  Various"  Class. 

SECTION  IV.  — Turkeys,  Orna- 
mental Poultry,  and  Water- 
Fowl. 

Chap.  XXII.— Turkeys,  Guinea-fowl, 

Pea-fowl. 
Chap.  XXIII.— Pheasants. 
Chap.  XXIV.— Water-fowl. 

SECTION  v.— The  Hatching  and 
Rearing  of  Chickens  Artifici- 
ally. 

Chap.  XXV.— The  Incubator  and  its 
Management. 

Chap.  XXVI.— Rearing  Chickens  Ar- 
tificially. 

SECTION  VI.— The  Breeding  and 
Management  of  Poultry  upon 
A  Large  Scale. 

Chap.  XXVII.— Separate  Establish- 
ments for  Rearing  Poultry.  Poul- 
try on  the  Farm.    Conclusion. 


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asure. 


A  GUIDE  TO  THE  AMATEUR  IN  THE 

Peuit,  VeC"31table,  and  FL077EE  Gaeden, 

WITH  rULL  DIRECTIONS  FOK  THE 

gheenhouse,  coksehvatoe-y,  and 

window-garden, 

By   Petee   Hendeesok. 

ATJTHOK  OF   "  GARUENIXa  FOR  PROFIT,"  AND  "  PRACTICAIi  FLOKICULTURE." 


Illustrated. 


EDITORIAL   NOTICES. 

One  of  the  most  popular  works  of  recent  years  on  similar  topics  was 
the  "Gardening  for  Profit"  of  Mr.  Peter  Henderson,  the  well-known 
florist  of  Jersey  City.  He  has  been  equally  fortunate  in  the  title  of  a  new 
book  from  his  pen,  just  published,  by  the  Orange  Judd  Co.,  of  New-York 
—"Gardening  for  Pleasure."  The  author  has  a  happy  faculty  of  writing 
for  the  most  part  just  what  people  want  to  know — so  that,  although' his 
books  are  neither  exhaustive  ror  especially  elaborate,  they  proceed  to  the 
gist  of  the  subject  in  hand  Vv'ith  so  much  directness  and  simplicity  that  they 
till  a  most  important  and  useful  sphere  in  our  rural  literature. — T/ie  Culti- 
tator  and  Country  Gentleman,  Albany,  N,  Y. 

It  gives,  in  a  clear,  intelligible  form,  just  the  information  that  novices 
and  even  experienced  cultivators  wish  to  have  always  accessible,  and  will 
be  specially  valuable  to  those  who  keep  house  plants. — 27ie  Ooserver,  New- 
York  City. 

Mr.  Peter  Henderson  has  followed  up  "  Gardening  for  Profit"  with 
"  Gardening  for  Pleasure."  into  which  is  packed  much  useful  information 
about  window-gardens,  the  management  of  flower-beds,  etc. — The  Inde- 
pendent, Neiu-York  City. 

He  is  a  thoroughly  practical  man,  uses  plain,  common  language,  and 
not  technical  terms,  in  his  statements  and  explanations,  and  puts  the  staff 
of  knowledge  directly  into  the  hands  of  the  amateur  and  sets  him  at  work. 
—The  Press,  Providence,  E.  I. 

People  who  have  money  to  spend  in  adorning  their  grounds,  are  told 
here  how  to  do  it  to  the  best  advantage,  and  ladies  are  fully  instructed  in 
all  the  art  and  mystery  of  window-gardening.  It  will  prove  a  useful  guide 
to  all  who  have  a  taste  for  flowers,  and  also  contains  practical  instructions 
for  the  cultivation  of  fruits  and  vegetables.—  The  Transciipt,  Portland,  Me. 

This  volume  is  eminently  clear  in  its  style  and  practical  in  its  direc- 
tions. Its  appearance  is  timely,  as  it  contains  some  valuable  hints  upon 
winter  flowering  plants  and  their  proper  cultivation,  together  with  plain 
directions  how  to  raise  them  from  seed  and  to  multiply  them  by  cuttings. — 
Courier-Journal,  Louisville,  Ky. 

Price,  post-paid,  $1.50. 

ORANGE  JUDB  COMPANY, 

245  Broadway,  liTew-York, 


now   CROPS    GROW. 

On  tlie  Cleinical  CoBipsitioii,  StrEtire,  ai  Life  of  tie  Plant, 

FOR   ALL  STUDENTS  OF   AGRICULTURE. 

WITH  NUEIEROUS  ILLUSTRATIOIJS  AND  TABLES  OF  AMLYSE3. 

BY 

SAMUEE,    IV.    JOII^SOM,    M.A., 

PBf/FESSOR  OB"  ANALYTICAL  AND  AQRICtTLTUKAL  CHEMISTRY  IN  YALE  COLLEGE  ; 

CHEMIST  TO  THE  CONNECTICUT  STATE  AGRICULTURAL  SOCIETY  ; 

MEMBER  OF  THE  NATIONAL  ACADEMY  OF  SCIENCES. 

This  is  a  volume  of  nearly  400  pages,  in  wliicli  Agricultura] 
Plants,  or  "  Crops,"  are  considered  from  tliree  distinct,  yet  closely 
related,  stand-points,  as  indicated  by  the  descriptive  title. 

THE  CHEMICAL  COMPOSITION  OF  THE  PLiXT. 

Ut.—T7ie  Volatile  Part. 

2d. — Tlie  Ash — Its  Ingredients  ;  their  Distribution,  Variation,  and 
Quantities.  The  Composition  of  the  Ash  of  various  Farm 
Crops,  with  full  Tables  ;  and  the  Functions  of  the  Ash. 

8d. — Composition  of  the  Plant  in  'carious  Stages  of  Growth,  and  the 
Relations  subsisting  among  the  Ingredients. 

THE  STRUCTURE  OF  THE   PLANT  AND   THE   OFFICES 

OF  ITS  ORUANS. 

TJie  Primary  Elements  of  Organic  Structure. 

Tlie  Vegetative  Organs — Root,  Stem,  and  Leaf,  and  their  Func- 
lions ;  and 

The  Reproductive  Organs,  namely,  Flowers  and  Fruit,  and  th€ 
Vitality  of  Seeds  with  their  Influence  on  the  Plants  they  produce. 

THE  LIFE  OF  THE  PLiNT. 

Germination,  and  the  conditions  most  favorable  and  unfavor- 
Rble  to  it. 

The  Food  of  the  Plant  when  independent  of  the  Seed. 

Sap  and  its  Motions,  etc.,  etc. 

The  Appendix,  which  consists  of  twelve  Tables  exhibiting 
the  Composition  of  a  great  number  of  Plants  viewed  from  many 
diiferent  stand-points,  will  be  found  of  inestimable  value  to  piacti 
cal  ajfriculturists,  students,  and  theorists. 

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